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en/tutorials/css/9css-layout

# 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:

```css
/* 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:

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

### Relative

Offset from normal position:

```css
.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:

```css
.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:

```css
.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:

```css
.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):

```css
.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:

```css
/* 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

```css
/* 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;
}
```

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

## Complete Example: Modal Overlay

```css
/* 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;
}
```

```html
<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

```css
/* 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;
}
```

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

## Complete Example: Back to Top Button

```css
.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);
}
```

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

## Layout Techniques

### Centering

```css
/* 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

```css
/* 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

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