Code Notes made by Vaibhav Rathod

CSS

30 min read

Written by Makvana Smitrajsinh

History

  • How:
    • Developed by Håkon Wium Lie and Bert Bos in 1994 at W3C (World Wide Web Consortium).
    • Designed to separate content (HTML) from presentation (layout and style).
    • CSS1 released in 1996, CSS2 in 1998, CSS3 started in 1999 (modular approach).
    • CSS3 introduced animations, transitions, flexbox, grid, custom properties, and more.
  • Who:
    • Håkon Wium Lie — Norwegian web pioneer, creator of CSS, worked at CERN under Tim Berners-Lee.
    • Bert Bos — Dutch computer scientist, co-developer of CSS at W3C.
    • W3C (World Wide Web Consortium) — oversees CSS standards and development.
  • Why:
    • To allow web developers to create dynamic, consistent, and maintainable web designs.
    • To separate structure (HTML) from presentation (CSS) for better code organization.
    • To provide flexibility in styling, enabling responsive design and accessibility.
    • To reduce code redundancy by applying styles globally via classes and selectors.

Introduction

Advantages

  • Separation of Concerns — CSS separates HTML structure from visual styling.
  • Reusability — One stylesheet can style multiple pages.
  • Responsive Design — Media queries enable layouts for different screen sizes.
  • Animations & Transitions — Create smooth visual effects without JavaScript.
  • Cross-Browser Compatibility — Works across all modern browsers.
  • Customization — Extensive styling options for colors, fonts, layouts, effects.
  • Performance — External stylesheets are cached by browsers.
  • Maintainability — Centralized styling makes updates easier.

Disadvantages

  • No Logic — CSS lacks programming constructs (loops, conditions, variables in older versions).
  • Browser Inconsistencies — Older browsers may not support modern CSS features.
  • Specificity Conflicts — Complex selectors can lead to unexpected overrides.
  • Scalability Issues — Large CSS files can become difficult to manage without preprocessors.
  • Limited Layout Control — Older techniques (floats, positioning) are cumbersome.
  • Performance Issues — Complex animations and selectors can impact performance.

Basics

CSS Syntax & Structure

/* Selector { property: value; } */
 
h1 {
    color: blue;           /* Text color */
    font-size: 24px;       /* Font size */
    text-align: center;    /* Text alignment */
}
 
/* Multiple selectors */
h1, h2, h3 {
    font-family: Arial, sans-serif;
}
 
/* Comments */
/* This is a single-line comment */
 
/*
 * This is a
 * multi-line comment
 */

Three Ways to Add CSS

<!-- 1. Inline CSS (highest specificity, avoid for maintainability) -->
<p style="color: red; font-size: 16px;">Inline styled text</p>
 
<!-- 2. Internal CSS (in <head> section) -->
<head>
    <style>
        p {
            color: blue;
            font-size: 14px;
        }
    </style>
</head>
 
<!-- 3. External CSS (best practice) -->
<head>
    <link rel="stylesheet" href="styles.css">
</head>

CSS Selectors

/* Universal selector */
* {
    margin: 0;
    padding: 0;
}
 
/* Element selector */
p {
    color: black;
}
 
/* Class selector */
.highlight {
    background-color: yellow;
}
 
/* ID selector */
#header {
    background-color: navy;
}
 
/* Descendant selector (space) */
div p {
    color: red;  /* All <p> inside <div> */
}
 
/* Child selector (>) */
div > p {
    color: blue;  /* Direct <p> children of <div> */
}
 
/* Adjacent sibling selector (+) */
h1 + p {
    margin-top: 0;  /* <p> immediately after <h1> */
}
 
/* General sibling selector (~) */
h1 ~ p {
    color: gray;  /* All <p> siblings after <h1> */
}
 
/* Attribute selectors */
input[type="text"] {
    border: 1px solid #ccc;
}
 
a[href^="https"] {
    color: green;  /* Links starting with https */
}
 
a[href$=".pdf"] {
    color: red;  /* Links ending with .pdf */
}
 
a[href*="example"] {
    color: blue;  /* Links containing "example" */
}
 
/* Multiple classes */
.class1.class2 {
    font-weight: bold;  /* Elements with both classes */
}

Pseudo-classes

/* Link states */
a:link { color: blue; }
a:visited { color: purple; }
a:hover { color: red; }
a:active { color: orange; }
 
/* Form states */
input:focus { border-color: blue; }
input:disabled { background-color: #eee; }
input:checked { background-color: green; }
input:required { border-color: red; }
input:valid { border-color: green; }
input:invalid { border-color: red; }
 
/* Structural pseudo-classes */
li:first-child { font-weight: bold; }
li:last-child { margin-bottom: 0; }
li:nth-child(2) { color: red; }  /* 2nd child */
li:nth-child(odd) { background: #f0f0f0; }  /* Odd rows */
li:nth-child(even) { background: white; }   /* Even rows */
li:nth-child(3n) { color: blue; }  /* Every 3rd element */
 
p:first-of-type { font-size: 20px; }
p:last-of-type { margin-bottom: 0; }
p:nth-of-type(2) { color: green; }
 
/* Other useful pseudo-classes */
div:empty { display: none; }  /* Empty elements */
p:not(.special) { color: gray; }  /* All <p> except .special */
:root { --main-color: blue; }  /* Root element (for CSS variables) */

Pseudo-elements

/* ::before and ::after */
p::before {
    content: "→ ";
    color: blue;
}
 
p::after {
    content: " ←";
    color: red;
}
 
/* First letter and first line */
p::first-letter {
    font-size: 2em;
    font-weight: bold;
    color: red;
}
 
p::first-line {
    font-variant: small-caps;
}
 
/* Selection styling */
::selection {
    background-color: yellow;
    color: black;
}
 
/* Placeholder styling */
input::placeholder {
    color: #999;
    font-style: italic;
}

Colors & Units

/* Color formats */
.color-examples {
    /* Named colors */
    color: red;
    
    /* Hexadecimal */
    color: #ff0000;
    color: #f00;  /* Shorthand */
    
    /* RGB */
    color: rgb(255, 0, 0);
    
    /* RGBA (with alpha/transparency) */
    color: rgba(255, 0, 0, 0.5);  /* 50% transparent */
    
    /* HSL (Hue, Saturation, Lightness) */
    color: hsl(0, 100%, 50%);
    
    /* HSLA (with alpha) */
    color: hsla(0, 100%, 50%, 0.5);
}
 
/* Length units */
.units {
    /* Absolute units */
    width: 100px;    /* Pixels */
    width: 2cm;      /* Centimeters */
    width: 1in;      /* Inches */
    
    /* Relative units */
    font-size: 1em;     /* Relative to parent font size */
    font-size: 1rem;    /* Relative to root font size */
    width: 50%;         /* Percentage of parent */
    width: 50vw;        /* 50% of viewport width */
    height: 100vh;      /* 100% of viewport height */
    font-size: 2vmin;   /* 2% of smaller viewport dimension */
    font-size: 2vmax;   /* 2% of larger viewport dimension */
    width: 10ch;        /* Width of 10 "0" characters */
    line-height: 1.5ex; /* Height of "x" character */
}

Box Model & Layout

Box Model

/* Box model components: content, padding, border, margin */
 
.box {
    width: 300px;
    height: 200px;
    padding: 20px;           /* Space inside border */
    border: 5px solid black; /* Border around padding */
    margin: 10px;            /* Space outside border */
}
 
/* Individual sides */
.box {
    padding-top: 10px;
    padding-right: 20px;
    padding-bottom: 10px;
    padding-left: 20px;
    
    /* Shorthand: top right bottom left (clockwise) */
    padding: 10px 20px 10px 20px;
    padding: 10px 20px;  /* vertical horizontal */
    padding: 10px;       /* all sides */
}
 
/* Box-sizing */
* {
    box-sizing: border-box;  /* Include padding and border in width/height */
}
 
/* Default is content-box */
.content-box {
    box-sizing: content-box;  /* Width/height only applies to content */
}

Display Property

/* Block elements (take full width, start on new line) */
div {
    display: block;
}
 
/* Inline elements (only take necessary width, no line break) */
span {
    display: inline;
}
 
/* Inline-block (inline but can have width/height) */
.button {
    display: inline-block;
    width: 100px;
    height: 40px;
}
 
/* Hide element */
.hidden {
    display: none;  /* Removes from layout */
}
 
/* Visibility (keeps space) */
.invisible {
    visibility: hidden;  /* Hidden but space remains */
}
 
/* Flex container */
.flex-container {
    display: flex;
}
 
/* Grid container */
.grid-container {
    display: grid;
}

Position Property

/* Static (default) */
.static {
    position: static;  /* Normal document flow */
}
 
/* Relative (relative to normal position) */
.relative {
    position: relative;
    top: 10px;    /* Move 10px down from normal position */
    left: 20px;   /* Move 20px right from normal position */
}
 
/* Absolute (relative to nearest positioned ancestor) */
.absolute {
    position: absolute;
    top: 0;
    right: 0;  /* Position at top-right of parent */
}
 
/* Fixed (relative to viewport, stays on scroll) */
.fixed {
    position: fixed;
    bottom: 20px;
    right: 20px;  /* Fixed at bottom-right of screen */
}
 
/* Sticky (hybrid of relative and fixed) */
.sticky {
    position: sticky;
    top: 0;  /* Sticks to top when scrolling */
}
 
/* Z-index (stacking order) */
.layer1 { z-index: 1; }
.layer2 { z-index: 2; }  /* Appears above layer1 */
.layer3 { z-index: 999; }

Float & Clear

/* Float (older layout technique) */
.left {
    float: left;
    width: 50%;
}
 
.right {
    float: right;
    width: 50%;
}
 
/* Clear floats */
.clear {
    clear: both;  /* Clear both left and right floats */
}
 
/* Clearfix hack (for parent of floated elements) */
.clearfix::after {
    content: "";
    display: table;
    clear: both;
}

Overflow

.container {
    width: 200px;
    height: 100px;
    overflow: visible;  /* Default, content overflows */
    overflow: hidden;   /* Hide overflow */
    overflow: scroll;   /* Always show scrollbars */
    overflow: auto;     /* Scrollbars only when needed */
}
 
/* Separate horizontal and vertical */
.box {
    overflow-x: hidden;
    overflow-y: scroll;
}

Flexbox

Flex Container Properties

.container {
    display: flex;  /* Enable flexbox */
    
    /* Direction */
    flex-direction: row;          /* Default: left to right */
    flex-direction: row-reverse;  /* Right to left */
    flex-direction: column;       /* Top to bottom */
    flex-direction: column-reverse; /* Bottom to top */
    
    /* Wrap */
    flex-wrap: nowrap;   /* Default: single line */
    flex-wrap: wrap;     /* Multi-line */
    flex-wrap: wrap-reverse;
    
    /* Shorthand for direction and wrap */
    flex-flow: row wrap;
    
    /* Justify content (main axis alignment) */
    justify-content: flex-start;    /* Default: start */
    justify-content: flex-end;      /* End */
    justify-content: center;        /* Center */
    justify-content: space-between; /* Equal space between items */
    justify-content: space-around;  /* Equal space around items */
    justify-content: space-evenly;  /* Equal space everywhere */
    
    /* Align items (cross axis alignment) */
    align-items: stretch;     /* Default: stretch to fill */
    align-items: flex-start;  /* Top */
    align-items: flex-end;    /* Bottom */
    align-items: center;      /* Center */
    align-items: baseline;    /* Align baselines */
    
    /* Align content (multi-line cross axis) */
    align-content: flex-start;
    align-content: flex-end;
    align-content: center;
    align-content: space-between;
    align-content: space-around;
    align-content: stretch;
    
    /* Gap between items */
    gap: 20px;           /* Both row and column gap */
    row-gap: 10px;       /* Gap between rows */
    column-gap: 20px;    /* Gap between columns */
}

Flex Item Properties

.item {
    /* Order (default is 0) */
    order: 1;  /* Higher values appear later */
    
    /* Flex grow (how much item grows relative to others) */
    flex-grow: 0;  /* Default: don't grow */
    flex-grow: 1;  /* Grow to fill space */
    flex-grow: 2;  /* Grow twice as much as flex-grow: 1 */
    
    /* Flex shrink (how much item shrinks) */
    flex-shrink: 1;  /* Default: can shrink */
    flex-shrink: 0;  /* Don't shrink */
    
    /* Flex basis (initial size before growing/shrinking) */
    flex-basis: auto;   /* Default: based on content */
    flex-basis: 200px;  /* Fixed initial size */
    flex-basis: 50%;    /* Percentage of container */
    
    /* Shorthand: flex-grow flex-shrink flex-basis */
    flex: 0 1 auto;  /* Default */
    flex: 1;         /* flex: 1 1 0 (grow, shrink, 0 basis) */
    flex: 2;         /* Grow twice as much */
    flex: 0 0 200px; /* Fixed 200px, no grow/shrink */
    
    /* Align self (override container's align-items) */
    align-self: auto;       /* Default: inherit from container */
    align-self: flex-start;
    align-self: flex-end;
    align-self: center;
    align-self: baseline;
    align-self: stretch;
}

Flexbox Examples

/* Centered content */
.center-box {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}
 
/* Navigation bar */
.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
}
 
/* Equal width columns */
.columns {
    display: flex;
    gap: 20px;
}
.columns > div {
    flex: 1;  /* All columns equal width */
}
 
/* Responsive card layout */
.card-container {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
}
.card {
    flex: 1 1 300px;  /* Grow, shrink, min 300px */
}

CSS Grid

Grid Container Properties

.grid-container {
    display: grid;
    
    /* Define columns */
    grid-template-columns: 200px 200px 200px;  /* 3 fixed columns */
    grid-template-columns: 1fr 1fr 1fr;        /* 3 equal columns */
    grid-template-columns: 1fr 2fr 1fr;        /* Middle column twice as wide */
    grid-template-columns: repeat(3, 1fr);     /* Repeat 3 times */
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); /* Responsive */
    
    /* Define rows */
    grid-template-rows: 100px 200px 100px;
    grid-template-rows: repeat(3, 1fr);
    
    /* Gap between grid items */
    gap: 20px;              /* Both row and column gap */
    row-gap: 10px;          /* Gap between rows */
    column-gap: 20px;       /* Gap between columns */
    
    /* Justify items (horizontal alignment within cell) */
    justify-items: start;   /* Left */
    justify-items: end;     /* Right */
    justify-items: center;  /* Center */
    justify-items: stretch; /* Default: fill cell */
    
    /* Align items (vertical alignment within cell) */
    align-items: start;     /* Top */
    align-items: end;       /* Bottom */
    align-items: center;    /* Center */
    align-items: stretch;   /* Default: fill cell */
    
    /* Justify content (align entire grid horizontally) */
    justify-content: start;
    justify-content: end;
    justify-content: center;
    justify-content: space-between;
    justify-content: space-around;
    justify-content: space-evenly;
    
    /* Align content (align entire grid vertically) */
    align-content: start;
    align-content: end;
    align-content: center;
    align-content: space-between;
    align-content: space-around;
    align-content: space-evenly;
}

Grid Item Properties

.grid-item {
    /* Column placement */
    grid-column-start: 1;
    grid-column-end: 3;      /* Span from column 1 to 3 */
    grid-column: 1 / 3;      /* Shorthand */
    grid-column: 1 / span 2; /* Start at 1, span 2 columns */
    
    /* Row placement */
    grid-row-start: 1;
    grid-row-end: 3;
    grid-row: 1 / 3;         /* Shorthand */
    grid-row: 1 / span 2;    /* Start at 1, span 2 rows */
    
    /* Area shorthand: row-start / col-start / row-end / col-end */
    grid-area: 1 / 1 / 3 / 3;
    
    /* Justify self (override container's justify-items) */
    justify-self: start;
    justify-self: end;
    justify-self: center;
    justify-self: stretch;
    
    /* Align self (override container's align-items) */
    align-self: start;
    align-self: end;
    align-self: center;
    align-self: stretch;
}

Grid Template Areas

.grid-layout {
    display: grid;
    grid-template-columns: 1fr 3fr 1fr;
    grid-template-rows: auto 1fr auto;
    grid-template-areas:
        "header header header"
        "sidebar main aside"
        "footer footer footer";
    gap: 10px;
}
 
.header  { grid-area: header; }
.sidebar { grid-area: sidebar; }
.main    { grid-area: main; }
.aside   { grid-area: aside; }
.footer  { grid-area: footer; }

Grid Examples

/* Simple 3-column layout */
.three-columns {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}
 
/* Responsive grid (auto-fit) */
.responsive-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
}
 
/* Holy Grail Layout */
.holy-grail {
    display: grid;
    grid-template-columns: 200px 1fr 200px;
    grid-template-rows: auto 1fr auto;
    min-height: 100vh;
}
 
/* Card spanning multiple columns */
.featured-card {
    grid-column: span 2;
    grid-row: span 2;
}

Typography & Text Styling

Font Properties

.text {
    /* Font family */
    font-family: Arial, Helvetica, sans-serif;
    font-family: 'Times New Roman', serif;
    font-family: 'Courier New', monospace;
    
    /* Font size */
    font-size: 16px;
    font-size: 1rem;
    font-size: 1.5em;
    
    /* Font weight */
    font-weight: normal;   /* 400 */
    font-weight: bold;     /* 700 */
    font-weight: 100;      /* Thin */
    font-weight: 900;      /* Black */
    
    /* Font style */
    font-style: normal;
    font-style: italic;
    font-style: oblique;
    
    /* Font variant */
    font-variant: normal;
    font-variant: small-caps;
    
    /* Line height */
    line-height: 1.5;      /* Relative to font size */
    line-height: 24px;     /* Fixed */
    
    /* Shorthand: style variant weight size/line-height family */
    font: italic small-caps bold 16px/1.5 Arial, sans-serif;
}

Text Properties

.text-styling {
    /* Color */
    color: #333;
    
    /* Alignment */
    text-align: left;
    text-align: right;
    text-align: center;
    text-align: justify;
    
    /* Decoration */
    text-decoration: none;
    text-decoration: underline;
    text-decoration: overline;
    text-decoration: line-through;
    text-decoration: underline wavy red;
    
    /* Transform */
    text-transform: none;
    text-transform: uppercase;
    text-transform: lowercase;
    text-transform: capitalize;
    
    /* Indent */
    text-indent: 50px;
    
    /* Letter spacing */
    letter-spacing: 2px;
    letter-spacing: 0.1em;
    
    /* Word spacing */
    word-spacing: 5px;
    
    /* White space */
    white-space: normal;    /* Default */
    white-space: nowrap;    /* No wrapping */
    white-space: pre;       /* Preserve whitespace */
    white-space: pre-wrap;  /* Preserve + wrap */
    
    /* Text overflow */
    text-overflow: clip;
    text-overflow: ellipsis; /* ... */
    
    /* Word break */
    word-break: normal;
    word-break: break-all;
    word-break: keep-all;
    
    /* Text shadow */
    text-shadow: 2px 2px 4px rgba(0,0,0,0.5);
    text-shadow: 0 0 10px #fff, 0 0 20px #fff; /* Glow effect */
}

Web Fonts (Google Fonts)

<!-- In HTML <head> -->
<link rel="preconnect" href="https://fonts.googleapis.com">
<link href="https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap" rel="stylesheet">
/* In CSS */
body {
    font-family: 'Roboto', sans-serif;
}
 
/* @font-face for custom fonts */
@font-face {
    font-family: 'CustomFont';
    src: url('fonts/custom.woff2') format('woff2'),
         url('fonts/custom.woff') format('woff');
    font-weight: normal;
    font-style: normal;
    font-display: swap; /* Improve loading performance */
}
 
.custom-text {
    font-family: 'CustomFont', sans-serif;
}

Text Truncation with Ellipsis

/* Single line truncation */
.truncate {
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    max-width: 200px;
}
 
/* Multi-line truncation (webkit only) */
.truncate-multiline {
    display: -webkit-box;
    -webkit-line-clamp: 3;  /* Number of lines */
    -webkit-box-orient: vertical;
    overflow: hidden;
}

Backgrounds & Borders

Background Properties

.background {
    /* Background color */
    background-color: #f0f0f0;
    background-color: rgba(255, 0, 0, 0.5);
    
    /* Background image */
    background-image: url('image.jpg');
    background-image: linear-gradient(to right, red, blue);
    background-image: radial-gradient(circle, red, blue);
    
    /* Background repeat */
    background-repeat: repeat;      /* Default */
    background-repeat: no-repeat;
    background-repeat: repeat-x;    /* Horizontal only */
    background-repeat: repeat-y;    /* Vertical only */
    
    /* Background position */
    background-position: center;
    background-position: top left;
    background-position: 50% 50%;
    background-position: 10px 20px;
    
    /* Background size */
    background-size: auto;          /* Default */
    background-size: cover;         /* Cover entire element */
    background-size: contain;       /* Fit inside element */
    background-size: 100px 200px;   /* Fixed size */
    background-size: 50% 50%;       /* Percentage */
    
    /* Background attachment */
    background-attachment: scroll;  /* Default */
    background-attachment: fixed;   /* Fixed to viewport */
    background-attachment: local;   /* Scrolls with content */
    
    /* Background origin */
    background-origin: padding-box; /* Default */
    background-origin: border-box;
    background-origin: content-box;
    
    /* Background clip */
    background-clip: border-box;    /* Default */
    background-clip: padding-box;
    background-clip: content-box;
    background-clip: text;          /* Clip to text (webkit) */
    
    /* Shorthand: color image repeat position / size */
    background: #f0f0f0 url('bg.jpg') no-repeat center / cover;
}
 
/* Multiple backgrounds */
.multi-bg {
    background-image: url('front.png'), url('back.jpg');
    background-position: center, top left;
    background-repeat: no-repeat, repeat;
}
 
/* Gradient backgrounds */
.gradient {
    /* Linear gradient */
    background: linear-gradient(to right, #ff0000, #0000ff);
    background: linear-gradient(45deg, red, yellow, green);
    background: linear-gradient(to bottom, rgba(0,0,0,0), rgba(0,0,0,1));
    
    /* Radial gradient */
    background: radial-gradient(circle, red, blue);
    background: radial-gradient(ellipse at top, red, blue);
    
    /* Repeating gradients */
    background: repeating-linear-gradient(45deg, red, red 10px, blue 10px, blue 20px);
}

Border Properties

.border {
    /* Border width */
    border-width: 1px;
    border-width: 2px 4px;          /* vertical horizontal */
    border-width: 1px 2px 3px 4px;  /* top right bottom left */
    
    /* Border style */
    border-style: solid;
    border-style: dashed;
    border-style: dotted;
    border-style: double;
    border-style: groove;
    border-style: ridge;
    border-style: inset;
    border-style: outset;
    border-style: none;
    border-style: hidden;
    
    /* Border color */
    border-color: #000;
    border-color: red blue green yellow; /* top right bottom left */
    
    /* Shorthand: width style color */
    border: 2px solid #333;
    
    /* Individual sides */
    border-top: 1px solid red;
    border-right: 2px dashed blue;
    border-bottom: 3px dotted green;
    border-left: 4px double yellow;
    
    /* Border radius (rounded corners) */
    border-radius: 10px;            /* All corners */
    border-radius: 10px 20px;       /* top-left/bottom-right, top-right/bottom-left */
    border-radius: 10px 20px 30px 40px; /* top-left, top-right, bottom-right, bottom-left */
    border-radius: 50%;             /* Circle */
    
    /* Individual corner radius */
    border-top-left-radius: 10px;
    border-top-right-radius: 20px;
    border-bottom-right-radius: 30px;
    border-bottom-left-radius: 40px;
    
    /* Elliptical corners */
    border-radius: 50px / 25px;     /* horizontal / vertical */
}

Outline (Outside Border)

.outline {
    outline: 2px solid blue;
    outline-width: 3px;
    outline-style: dashed;
    outline-color: red;
    outline-offset: 5px;  /* Space between border and outline */
    
    /* Remove default focus outline */
    outline: none;  /* Use carefully, provide alternative focus indicator */
}

Box Shadow

.shadow {
    /* box-shadow: horizontal vertical blur spread color */
    box-shadow: 5px 5px 10px rgba(0,0,0,0.3);
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    
    /* Inset shadow */
    box-shadow: inset 0 0 10px rgba(0,0,0,0.5);
    
    /* Multiple shadows */
    box-shadow: 
        0 2px 4px rgba(0,0,0,0.1),
        0 4px 8px rgba(0,0,0,0.1),
        0 8px 16px rgba(0,0,0,0.1);
    
    /* No shadow */
    box-shadow: none;
}

Transitions & Animations

CSS Transitions

.transition {
    /* Transition property */
    transition-property: all;           /* All properties */
    transition-property: background-color;
    transition-property: width, height; /* Multiple properties */
    
    /* Transition duration */
    transition-duration: 0.3s;
    transition-duration: 300ms;
    
    /* Transition timing function */
    transition-timing-function: ease;        /* Default */
    transition-timing-function: linear;
    transition-timing-function: ease-in;
    transition-timing-function: ease-out;
    transition-timing-function: ease-in-out;
    transition-timing-function: cubic-bezier(0.1, 0.7, 1.0, 0.1);
    
    /* Transition delay */
    transition-delay: 0s;
    transition-delay: 0.5s;
    
    /* Shorthand: property duration timing-function delay */
    transition: all 0.3s ease 0s;
    transition: background-color 0.5s ease-in-out;
    transition: width 0.3s, height 0.3s, background 0.5s;
}
 
/* Example: Button hover transition */
.button {
    background-color: blue;
    color: white;
    padding: 10px 20px;
    transition: all 0.3s ease;
}
 
.button:hover {
    background-color: darkblue;
    transform: scale(1.05);
}

CSS Animations

/* Define keyframes */
@keyframes slide-in {
    from {
        transform: translateX(-100%);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}
 
/* Percentage keyframes */
@keyframes bounce {
    0% { transform: translateY(0); }
    50% { transform: translateY(-20px); }
    100% { transform: translateY(0); }
}
 
/* Apply animation */
.animated {
    /* Animation name */
    animation-name: slide-in;
    
    /* Animation duration */
    animation-duration: 1s;
    
    /* Animation timing function */
    animation-timing-function: ease-in-out;
    
    /* Animation delay */
    animation-delay: 0.5s;
    
    /* Animation iteration count */
    animation-iteration-count: 1;       /* Once */
    animation-iteration-count: 3;       /* 3 times */
    animation-iteration-count: infinite; /* Forever */
    
    /* Animation direction */
    animation-direction: normal;        /* Default */
    animation-direction: reverse;       /* Backwards */
    animation-direction: alternate;     /* Forward then backward */
    animation-direction: alternate-reverse;
    
    /* Animation fill mode */
    animation-fill-mode: none;          /* Default */
    animation-fill-mode: forwards;      /* Keep final state */
    animation-fill-mode: backwards;     /* Apply first keyframe before start */
    animation-fill-mode: both;          /* Both forwards and backwards */
    
    /* Animation play state */
    animation-play-state: running;      /* Default */
    animation-play-state: paused;       /* Pause animation */
    
    /* Shorthand: name duration timing-function delay iteration-count direction fill-mode */
    animation: slide-in 1s ease-in-out 0.5s 1 normal forwards;
}
 
/* Pause on hover */
.animated:hover {
    animation-play-state: paused;
}

Animation Examples

/* Fade in */
@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}
.fade-in {
    animation: fadeIn 1s ease-in;
}
 
/* Spin */
@keyframes spin {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}
.spinner {
    animation: spin 2s linear infinite;
}
 
/* Pulse */
@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.1); }
}
.pulse {
    animation: pulse 1s ease-in-out infinite;
}
 
/* Shake */
@keyframes shake {
    0%, 100% { transform: translateX(0); }
    10%, 30%, 50%, 70%, 90% { transform: translateX(-10px); }
    20%, 40%, 60%, 80% { transform: translateX(10px); }
}
.shake {
    animation: shake 0.5s;
}
 
/* Loading dots */
@keyframes blink {
    0%, 100% { opacity: 0; }
    50% { opacity: 1; }
}
.dot {
    animation: blink 1.4s infinite;
}
.dot:nth-child(2) { animation-delay: 0.2s; }
.dot:nth-child(3) { animation-delay: 0.4s; }

Transforms

2D Transforms

.transform {
    /* Translate (move) */
    transform: translate(50px, 100px);  /* x, y */
    transform: translateX(50px);
    transform: translateY(100px);
    
    /* Scale (resize) */
    transform: scale(1.5);              /* Uniform scaling */
    transform: scale(2, 0.5);           /* x, y */
    transform: scaleX(2);
    transform: scaleY(0.5);
    
    /* Rotate */
    transform: rotate(45deg);
    transform: rotate(-90deg);
    transform: rotate(0.5turn);         /* Half turn */
    
    /* Skew (distort) */
    transform: skew(20deg, 10deg);      /* x, y */
    transform: skewX(20deg);
    transform: skewY(10deg);
    
    /* Multiple transforms */
    transform: translate(50px, 100px) rotate(45deg) scale(1.5);
    
    /* Transform origin (pivot point) */
    transform-origin: center;           /* Default */
    transform-origin: top left;
    transform-origin: 50% 50%;
    transform-origin: 100px 200px;
}

3D Transforms

.transform-3d {
    /* Perspective (depth) */
    perspective: 1000px;
    
    /* 3D translate */
    transform: translate3d(50px, 100px, 200px);
    transform: translateZ(100px);
    
    /* 3D rotate */
    transform: rotateX(45deg);
    transform: rotateY(45deg);
    transform: rotateZ(45deg);
    transform: rotate3d(1, 1, 0, 45deg);
    
    /* 3D scale */
    transform: scale3d(2, 2, 2);
    transform: scaleZ(2);
    
    /* Transform style (preserve 3D) */
    transform-style: flat;              /* Default */
    transform-style: preserve-3d;       /* Children in 3D space */
    
    /* Backface visibility */
    backface-visibility: visible;       /* Default */
    backface-visibility: hidden;        /* Hide back face */
}
 
/* 3D Card Flip Example */
.card-container {
    perspective: 1000px;
}
 
.card {
    transform-style: preserve-3d;
    transition: transform 0.6s;
}
 
.card:hover {
    transform: rotateY(180deg);
}
 
.card-front, .card-back {
    backface-visibility: hidden;
}
 
.card-back {
    transform: rotateY(180deg);
}

Responsive Design & Media Queries

Media Queries

/* Basic media query syntax */
@media media-type and (condition) {
    /* CSS rules */
}
 
/* Screen width breakpoints */
@media (max-width: 768px) {
    /* Styles for screens 768px and smaller (mobile) */
    .container {
        width: 100%;
        padding: 10px;
    }
}
 
@media (min-width: 769px) and (max-width: 1024px) {
    /* Styles for tablets (769px to 1024px) */
    .container {
        width: 90%;
    }
}
 
@media (min-width: 1025px) {
    /* Styles for desktops (1025px and larger) */
    .container {
        width: 1200px;
        margin: 0 auto;
    }
}
 
/* Common breakpoints */
/* Mobile: 320px - 480px */
/* Tablet: 481px - 768px */
/* Laptop: 769px - 1024px */
/* Desktop: 1025px - 1200px */
/* Large Desktop: 1201px+ */
 
/* Orientation */
@media (orientation: portrait) {
    /* Vertical orientation */
}
 
@media (orientation: landscape) {
    /* Horizontal orientation */
}
 
/* Device pixel ratio (retina displays) */
@media (-webkit-min-device-pixel-ratio: 2),
       (min-resolution: 192dpi) {
    /* High DPI displays */
    .logo {
        background-image: url('logo@2x.png');
    }
}
 
/* Print styles */
@media print {
    .no-print {
        display: none;
    }
    body {
        color: black;
        background: white;
    }
}
 
/* Hover capability */
@media (hover: hover) {
    /* Device supports hover (desktop) */
    .button:hover {
        background-color: blue;
    }
}
 
@media (hover: none) {
    /* Device doesn't support hover (touch) */
    .button:active {
        background-color: blue;
    }
}
 
/* Prefers color scheme (dark mode) */
@media (prefers-color-scheme: dark) {
    body {
        background-color: #1a1a1a;
        color: #ffffff;
    }
}
 
@media (prefers-color-scheme: light) {
    body {
        background-color: #ffffff;
        color: #000000;
    }
}
 
/* Reduced motion (accessibility) */
@media (prefers-reduced-motion: reduce) {
    * {
        animation: none !important;
        transition: none !important;
    }
}

Responsive Units

.responsive {
    /* Viewport units */
    width: 100vw;      /* 100% of viewport width */
    height: 100vh;     /* 100% of viewport height */
    font-size: 5vw;    /* 5% of viewport width */
    
    /* Relative units */
    font-size: 1rem;   /* Relative to root font size */
    padding: 2em;      /* Relative to element's font size */
    width: 50%;        /* Percentage of parent */
    
    /* Minimum and maximum */
    width: min(90%, 1200px);  /* Smaller of the two */
    width: max(300px, 50%);   /* Larger of the two */
    width: clamp(300px, 50%, 1200px); /* Between min and max */
}

Mobile-First Approach

/* Base styles (mobile) */
.container {
    width: 100%;
    padding: 15px;
}
 
/* Tablet and up */
@media (min-width: 768px) {
    .container {
        width: 750px;
        margin: 0 auto;
    }
}
 
/* Desktop and up */
@media (min-width: 1024px) {
    .container {
        width: 1000px;
    }
}
 
/* Large desktop */
@media (min-width: 1200px) {
    .container {
        width: 1170px;
    }
}

Container Queries (Modern CSS)

/* Container query (based on parent size, not viewport) */
.card-container {
    container-type: inline-size;
    container-name: card;
}
 
@container card (min-width: 400px) {
    .card {
        display: flex;
        flex-direction: row;
    }
}
 
@container card (max-width: 399px) {
    .card {
        display: flex;
        flex-direction: column;
    }
}

CSS Variables (Custom Properties)

Defining and Using Variables

/* Define variables in :root (global scope) */
:root {
    --primary-color: #3498db;
    --secondary-color: #2ecc71;
    --font-size: 16px;
    --spacing: 20px;
    --border-radius: 8px;
    --transition-speed: 0.3s;
}
 
/* Use variables with var() */
.button {
    background-color: var(--primary-color);
    font-size: var(--font-size);
    padding: var(--spacing);
    border-radius: var(--border-radius);
    transition: all var(--transition-speed);
}
 
/* Fallback value */
.element {
    color: var(--text-color, #000);  /* Use #000 if --text-color not defined */
}
 
/* Scoped variables */
.dark-theme {
    --primary-color: #1a1a1a;
    --text-color: #ffffff;
}
 
.light-theme {
    --primary-color: #ffffff;
    --text-color: #000000;
}

Dynamic Theme Switching

/* Light theme (default) */
:root {
    --bg-color: #ffffff;
    --text-color: #000000;
    --border-color: #cccccc;
}
 
/* Dark theme */
[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --text-color: #ffffff;
    --border-color: #444444;
}
 
/* Apply variables */
body {
    background-color: var(--bg-color);
    color: var(--text-color);
}
 
.card {
    border: 1px solid var(--border-color);
}
// Toggle theme with JavaScript
const toggleTheme = () => {
    const currentTheme = document.documentElement.getAttribute('data-theme');
    const newTheme = currentTheme === 'dark' ? 'light' : 'dark';
    document.documentElement.setAttribute('data-theme', newTheme);
};
 
// Set CSS variable dynamically
document.documentElement.style.setProperty('--primary-color', '#ff0000');

Calculations with Variables

:root {
    --base-size: 16px;
    --multiplier: 2;
}
 
.element {
    /* Use calc() with variables */
    font-size: calc(var(--base-size) * var(--multiplier));
    padding: calc(var(--base-size) / 2);
    margin: calc(var(--base-size) + 10px);
}

Advanced CSS Features

Filters

.filter-effects {
    /* Blur */
    filter: blur(5px);
    
    /* Brightness */
    filter: brightness(150%);  /* Brighter */
    filter: brightness(50%);   /* Darker */
    
    /* Contrast */
    filter: contrast(200%);
    
    /* Grayscale */
    filter: grayscale(100%);   /* Full grayscale */
    filter: grayscale(50%);    /* Partial */
    
    /* Hue rotate */
    filter: hue-rotate(90deg);
    
    /* Invert */
    filter: invert(100%);
    
    /* Opacity */
    filter: opacity(50%);
    
    /* Saturate */
    filter: saturate(200%);
    
    /* Sepia */
    filter: sepia(100%);
    
    /* Drop shadow */
    filter: drop-shadow(5px 5px 10px rgba(0,0,0,0.5));
    
    /* Multiple filters */
    filter: brightness(110%) contrast(120%) saturate(130%);
}
 
/* Backdrop filter (blur background) */
.glass-effect {
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
}

Clip Path

.clip-path {
    /* Circle */
    clip-path: circle(50%);
    clip-path: circle(100px at center);
    
    /* Ellipse */
    clip-path: ellipse(50% 30% at center);
    
    /* Polygon (custom shape) */
    clip-path: polygon(50% 0%, 100% 50%, 50% 100%, 0% 50%); /* Diamond */
    clip-path: polygon(0 0, 100% 0, 100% 80%, 0 100%);      /* Slanted */
    
    /* Inset (rectangle with rounded corners) */
    clip-path: inset(10px 20px 30px 40px round 10px);
}

Blend Modes

.blend-mode {
    /* Mix blend mode (blend with background) */
    mix-blend-mode: normal;
    mix-blend-mode: multiply;
    mix-blend-mode: screen;
    mix-blend-mode: overlay;
    mix-blend-mode: darken;
    mix-blend-mode: lighten;
    mix-blend-mode: color-dodge;
    mix-blend-mode: color-burn;
    mix-blend-mode: difference;
    mix-blend-mode: exclusion;
    
    /* Background blend mode */
    background-image: url('image.jpg'), linear-gradient(red, blue);
    background-blend-mode: multiply;
}

Object Fit & Object Position

img, video {
    /* Object fit (how content fits in container) */
    object-fit: fill;       /* Default: stretch to fill */
    object-fit: contain;    /* Fit inside, maintain aspect ratio */
    object-fit: cover;      /* Cover container, maintain aspect ratio */
    object-fit: none;       /* Original size */
    object-fit: scale-down; /* Smaller of none or contain */
    
    /* Object position */
    object-position: center;
    object-position: top left;
    object-position: 50% 50%;
    object-position: 10px 20px;
}

Scroll Snap

/* Scroll snap container */
.scroll-container {
    scroll-snap-type: y mandatory;  /* Vertical snapping */
    scroll-snap-type: x mandatory;  /* Horizontal snapping */
    scroll-snap-type: both mandatory;
    overflow-y: scroll;
    height: 100vh;
}
 
/* Scroll snap items */
.scroll-item {
    scroll-snap-align: start;   /* Snap to start */
    scroll-snap-align: center;  /* Snap to center */
    scroll-snap-align: end;     /* Snap to end */
    scroll-snap-stop: always;   /* Always stop at this item */
}

CSS Grid Auto-Placement

.masonry-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    grid-auto-rows: 10px;  /* Small row height */
    gap: 10px;
}
 
.masonry-item {
    grid-row-end: span 20;  /* Default span */
}
 
/* Adjust span based on content height with JavaScript */

Aspect Ratio

.aspect-ratio {
    /* Modern way (CSS aspect-ratio property) */
    aspect-ratio: 16 / 9;
    aspect-ratio: 1 / 1;  /* Square */
    aspect-ratio: 4 / 3;
    
    width: 100%;
    /* Height automatically calculated */
}
 
/* Old way (padding hack) */
.aspect-ratio-old {
    position: relative;
    width: 100%;
    padding-bottom: 56.25%;  /* 16:9 ratio (9/16 * 100) */
}
 
.aspect-ratio-old > * {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

CSS Best Practices & Performance

Specificity & Cascade

/* Specificity hierarchy (low to high):
 * 1. Element selectors (h1, div, p)
 * 2. Class selectors (.class)
 * 3. ID selectors (#id)
 * 4. Inline styles (style="...")
 * 5. !important (avoid unless necessary)
 */
 
/* Low specificity (good for reusability) */
.button { background: blue; }
 
/* Higher specificity */
.header .button { background: red; }
 
/* Even higher */
#main .header .button { background: green; }
 
/* Avoid !important */
.button { background: yellow !important; }  /* Hard to override */
 
/* Best practice: Keep specificity low */
.btn-primary { background: blue; }
.btn-secondary { background: gray; }

CSS Organization (BEM Methodology)

/* Block Element Modifier (BEM) naming convention */
 
/* Block */
.card { }
 
/* Element (part of block) */
.card__header { }
.card__body { }
.card__footer { }
 
/* Modifier (variation of block or element) */
.card--featured { }
.card--dark { }
.card__header--large { }
 
/* Example */
.button { }
.button--primary { }
.button--secondary { }
.button--large { }
.button__icon { }

Performance Optimization

/* Use efficient selectors */
/* Good */
.nav-item { }
 
/* Bad (slow) */
div > ul > li > a { }
 
/* Avoid universal selector in complex rules */
/* Bad */
* { box-sizing: border-box; }  /* OK at root level */
.container * { margin: 0; }   /* Avoid */
 
/* Use transform and opacity for animations (GPU accelerated) */
.animated {
    /* Good (GPU accelerated) */
    transform: translateX(100px);
    opacity: 0.5;
    
    /* Avoid animating these (causes reflow) */
    /* width, height, margin, padding, top, left */
}
 
/* Use will-change for heavy animations */
.heavy-animation {
    will-change: transform, opacity;
}
 
/* Remove will-change after animation */
.heavy-animation.done {
    will-change: auto;
}
 
/* Contain layout changes */
.isolated-component {
    contain: layout style paint;
}
 
/* Use content-visibility for off-screen content */
.long-list-item {
    content-visibility: auto;
    contain-intrinsic-size: 0 500px;  /* Estimated height */
}

Accessibility Best Practices

/* Ensure sufficient color contrast (WCAG AA: 4.5:1) */
.text {
    color: #333;
    background: #fff;
}
 
/* Visible focus indicators */
a:focus, button:focus {
    outline: 2px solid blue;
    outline-offset: 2px;
}
 
/* Don't remove outline without alternative */
/* Bad */
button:focus { outline: none; }
 
/* Good */
button:focus {
    outline: none;
    box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.5);
}
 
/* Respect user preferences */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}
 
/* Hidden but accessible to screen readers */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}
 
/* Minimum touch target size (44x44px) */
.button {
    min-width: 44px;
    min-height: 44px;
}

CSS Reset / Normalize

/* Simple CSS Reset */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
 
/* More comprehensive reset */
*, *::before, *::after {
    box-sizing: border-box;
}
 
body {
    margin: 0;
    font-family: system-ui, -apple-system, sans-serif;
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}
 
img, picture, video, canvas, svg {
    display: block;
    max-width: 100%;
}
 
input, button, textarea, select {
    font: inherit;
}
 
p, h1, h2, h3, h4, h5, h6 {
    overflow-wrap: break-word;
}

CSS Preprocessors & Tools

SASS/SCSS

// Variables
$primary-color: #3498db;
$font-stack: Arial, sans-serif;
 
// Nesting
.nav {
    background: $primary-color;
    
    ul {
        list-style: none;
        
        li {
            display: inline-block;
            
            a {
                color: white;
                
                &:hover {
                    text-decoration: underline;
                }
            }
        }
    }
}
 
// Mixins
@mixin flex-center {
    display: flex;
    justify-content: center;
    align-items: center;
}
 
.container {
    @include flex-center;
}
 
// Functions
@function calculate-rem($size) {
    @return $size / 16px * 1rem;
}
 
.text {
    font-size: calculate-rem(24px);
}
 
// Extend/Inheritance
%button-base {
    padding: 10px 20px;
    border: none;
    cursor: pointer;
}
 
.btn-primary {
    @extend %button-base;
    background: blue;
}
 
.btn-secondary {
    @extend %button-base;
    background: gray;
}

PostCSS

/* Autoprefixer automatically adds vendor prefixes */
.box {
    display: flex;  /* Autoprefixer adds -webkit-flex, etc. */
    transform: scale(1.5);
}
 
/* CSS Nesting (future CSS, available via PostCSS) */
.card {
    background: white;
    
    & .title {
        font-size: 24px;
    }
    
    &:hover {
        box-shadow: 0 4px 8px rgba(0,0,0,0.1);
    }
}

CSS Frameworks

  • Tailwind CSS — Utility-first CSS framework
<div class="flex items-center justify-center h-screen bg-blue-500">
    <h1 class="text-4xl font-bold text-white">Hello Tailwind</h1>
</div>
  • Bootstrap — Component-based framework
<button class="btn btn-primary">Primary Button</button>
<div class="container">
    <div class="row">
        <div class="col-md-6">Column 1</div>
        <div class="col-md-6">Column 2</div>
    </div>
</div>

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