css
The CSS Box Model
The box model is fundamental to understanding CSS layout. Every HTML element is treated as a rectangular box with content, padding, border, and margin.
Box Model Components
text
┌─────────────────────────────────────┐
│ MARGIN (transparent) │
│ ┌───────────────────────────────┐ │
│ │ BORDER │ │
│ │ ┌─────────────────────────┐ │ │
│ │ │ PADDING │ │ │
│ │ │ ┌───────────────────┐ │ │ │
│ │ │ │ CONTENT │ │ │ │
│ │ │ │ │ │ │ │
│ │ │ └───────────────────┘ │ │ │
│ │ └─────────────────────────┘ │ │
│ └───────────────────────────────┘ │
└─────────────────────────────────────┘Content
The actual content of the element (text, images, etc.):
css
.box {
width: 300px;
height: 200px;
}Padding
Space between the content and the border (inside the element):
css
/* All sides */
padding: 20px;
/* Vertical | Horizontal */
padding: 10px 20px;
/* Top | Horizontal | Bottom */
padding: 10px 20px 15px;
/* Top | Right | Bottom | Left */
padding: 10px 20px 15px 25px;
/* Individual sides */
padding-top: 10px;
padding-right: 20px;
padding-bottom: 15px;
padding-left: 25px;Border
The border around the padding and content:
css
/* Shorthand */
border: 2px solid black;
/* Individual properties */
border-width: 2px;
border-style: solid;
border-color: black;
/* Individual sides */
border-top: 1px solid red;
border-right: 2px dashed blue;
border-bottom: 3px dotted green;
border-left: 4px double orange;
/* Border radius (rounded corners) */
border-radius: 10px;
border-radius: 50%; /* Circle */
border-radius: 10px 20px 30px 40px; /* Each corner */Border Styles
css
border-style: solid; /* ──────── */
border-style: dashed; /* ─ ─ ─ ─ */
border-style: dotted; /* · · · · */
border-style: double; /* ════════ */
border-style: groove; /* 3D groove */
border-style: ridge; /* 3D ridge */
border-style: inset; /* 3D inset */
border-style: outset; /* 3D outset */
border-style: none; /* No border */Margin
Space outside the border (between elements):
css
/* All sides */
margin: 20px;
/* Vertical | Horizontal */
margin: 10px 20px;
/* Top | Horizontal | Bottom */
margin: 10px 20px 15px;
/* Top | Right | Bottom | Left */
margin: 10px 20px 15px 25px;
/* Individual sides */
margin-top: 10px;
margin-right: 20px;
margin-bottom: 15px;
margin-left: 25px;
/* Center an element */
margin: 0 auto;
/* Negative margins */
margin-top: -10px;Box Sizing
By default, width and height only apply to content. Use box-sizing to include padding and border:
css
/* Default behavior */
.box1 {
box-sizing: content-box;
width: 300px;
padding: 20px;
border: 5px solid black;
/* Total width: 300 + 40 + 10 = 350px */
}
/* Include padding and border in width */
.box2 {
box-sizing: border-box;
width: 300px;
padding: 20px;
border: 5px solid black;
/* Total width: 300px */
}
/* Apply to all elements (recommended) */
* {
box-sizing: border-box;
}Complete Example
html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Box Model Demo</title>
<style>
* {
box-sizing: border-box;
}
body {
font-family: Arial, sans-serif;
padding: 20px;
background-color: #f0f0f0;
}
.container {
max-width: 800px;
margin: 0 auto;
}
.box {
background-color: white;
width: 300px;
padding: 20px;
margin: 20px;
border: 3px solid #007bff;
border-radius: 8px;
}
.card {
background-color: white;
padding: 30px;
margin-bottom: 20px;
border: 1px solid #ddd;
border-radius: 10px;
box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}
.button {
display: inline-block;
padding: 12px 24px;
margin: 10px 5px;
border: 2px solid #007bff;
border-radius: 5px;
background-color: #007bff;
color: white;
text-decoration: none;
}
.button:hover {
background-color: white;
color: #007bff;
}
.spacing-demo {
background-color: lightblue;
padding: 20px;
margin: 30px 0;
border: 5px solid navy;
}
.spacing-demo p {
background-color: white;
padding: 15px;
margin: 10px 0;
border: 2px dashed gray;
}
</style>
</head>
<body>
<div class="container">
<h1>CSS Box Model</h1>
<div class="card">
<h2>What is the Box Model?</h2>
<p>Every element is a box with content, padding, border, and margin.</p>
</div>
<div class="box">
<h3>Example Box</h3>
<p>This box has 20px padding, 3px border, and 20px margin.</p>
</div>
<div class="card">
<h2>Buttons with Padding</h2>
<a href="#" class="button">Button 1</a>
<a href="#" class="button">Button 2</a>
<a href="#" class="button">Button 3</a>
</div>
<div class="spacing-demo">
<h3>Spacing Demo</h3>
<p>This paragraph has padding and margin.</p>
<p>So does this one!</p>
</div>
</div>
</body>
</html>Preview
Margin Collapse
Vertical margins between elements collapse to the larger of the two:
css
.box1 {
margin-bottom: 30px;
}
.box2 {
margin-top: 20px;
}
/* The space between box1 and box2 is 30px, not 50px */Display Property
The display property affects how the box model works:
css
/* Block elements (full width, stack vertically) */
display: block;
/* Inline elements (only as wide as content, flow horizontally) */
display: inline;
/* Inline-block (inline flow, but accepts width/height) */
display: inline-block;
/* Hide element */
display: none;