CSS Layout & Positioning

CSS positioning lets you place elements exactly where you want them. Understanding position types is essential for complex layouts.

Display Property

Controls how elements behave:

/* Block: Starts on new line, takes full width */
div {
  display: block;
}

/* Inline: Flows with text */
span {
  display: inline;
}

/* Inline-block: Flows inline but accepts width/height */
button {
  display: inline-block;
}

/* Flexbox */
.container {
  display: flex;
}

/* Grid */
.grid {
  display: grid;
}

/* Hide element */
.hidden {
  display: none;
}

Position Property

Static (Default)

Normal document flow:

.element {
  position: static; /* Default - no positioning */
}

Relative

Offset from normal position:

.element {
  position: relative;
  top: 10px;      /* 10px down from normal position */
  left: 20px;     /* 20px right from normal position */
  bottom: 5px;    /* 5px up from normal position */
  right: 10px;    /* 10px left from normal position */
}

Use for: Creating positioning context for children

Absolute

Removed from flow, positioned relative to nearest positioned ancestor:

.parent {
  position: relative; /* Creates positioning context */
}

.child {
  position: absolute;
  top: 0;
  right: 0;
  width: 100px;
  height: 100px;
}

Use for: Overlays, badges, icons

Fixed

Removed from flow, positioned relative to viewport:

.fixed-header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 100;
}

.back-to-top {
  position: fixed;
  bottom: 20px;
  right: 20px;
}

Use for: Sticky headers, floating buttons

Sticky

Hybrid of relative and fixed:

.sticky-nav {
  position: sticky;
  top: 0;
  background: white;
  z-index: 50;
}

Use for: Sticky navigation, table headers

Z-Index

Controls stacking order (higher = on top):

.front {
  position: absolute;
  z-index: 10;  /* On top */
}

.back {
  position: absolute;
  z-index: 1;   /* Behind */
}

Note: Only works on positioned elements (not static)

Overflow

Controls what happens when content exceeds container:

/* Hidden: Content is clipped */
.container {
  overflow: hidden;
}

/* Scroll: Always shows scrollbar */
.container {
  overflow: scroll;
}

/* Auto: Scrollbar only when needed */
.container {
  overflow: auto;
}

/* Individual axes */
.container {
  overflow-x: hidden;
  overflow-y: auto;
}

Complete Example: Sticky Header

/* Sticky header */
.header {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: #333;
  color: white;
  padding: 1rem 2rem;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
}

/* Page content */
.main {
  padding: 2rem;
  min-height: 100vh;
}

<header class="header">
  <h1>Sticky Header</h1>
</header>
<main class="main">
  <p>Scroll down to see sticky header...</p>
</main>

Complete Example: Modal Overlay

/* Modal overlay */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.7);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
}

/* Modal content */
.modal {
  background: white;
  padding: 2rem;
  border-radius: 10px;
  max-width: 500px;
  width: 90%;
  position: relative;
}

/* Close button */
.modal-close {
  position: absolute;
  top: 10px;
  right: 10px;
  background: none;
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
}

<div class="modal-overlay">
  <div class="modal">
    <button class="modal-close">×</button>
    <h2>Modal Title</h2>
    <p>Modal content goes here...</p>
  </div>
</div>

Complete Example: Tooltip

/* Tooltip container */
.tooltip {
  position: relative;
  display: inline-block;
}

/* Tooltip text */
.tooltip-text {
  position: absolute;
  bottom: 125%;
  left: 50%;
  transform: translateX(-50%);
  background-color: #333;
  color: white;
  padding: 5px 10px;
  border-radius: 5px;
  white-space: nowrap;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s;
}

/* Show tooltip on hover */
.tooltip:hover .tooltip-text {
  opacity: 1;
  visibility: visible;
}

<span class="tooltip">
  Hover me
  <span class="tooltip-text">This is a tooltip!</span>
</span>

Complete Example: Back to Top Button

.back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  width: 50px;
  height: 50px;
  background-color: #3498db;
  color: white;
  border: none;
  border-radius: 50%;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s, transform 0.3s;
  z-index: 99;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  transform: translateY(-5px);
}

<button class="back-to-top" onclick="window.scrollTo(0,0)">
  ↑
</button>

Layout Techniques

Centering

/* Flexbox centering */
.flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Grid centering */
.grid-center {
  display: grid;
  place-items: center;
}

/* Absolute centering */
.absolute-center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

Sticky Footer

/* Flexbox sticky footer */
body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  margin: 0;
}

main {
  flex: 1;
}

footer {
  padding: 1rem;
  background: #333;
  color: white;
}

Best Practices

1. Use flexbox/grid for layouts — Not positioning
2. Use position: fixed sparingly — Can cause scrolling issues
3. Always set z-index — Prevent stacking issues
4. Use transform for animations — Better performance
5. Test on mobile — Fixed elements behave differently

Common Mistakes

1. Using position for layouts — Use flexbox/grid instead
2. Forgetting z-index — Elements overlap unexpectedly
3. Not setting position on parent — Absolute children float away
4. Overusing fixed position — Causes scrolling problems
5. Ignoring transform — Better than top/left for animations