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CSS

CSS Overview Selectors Declarations Rule Sets Comments Reset/Normalize Origin Importance Order Specificity Inheritance Cascade Layers Inline Styles Internal Styles External Styles @import Absolute Units Relative Units Dynamic Viewport Angle Units Time Units Frequency Units: Resolution Units Keywords Color Formats Color Functions & Spaces Background Color Background Image Background Repeat Background Position Background Size Background Attachment Background Shorthand Multiple Backgrounds Linear Gradients Radial Gradients Conic Gradients Font Family Font Size Font Weight Font Style Line Height Text Align Text Decoration Text Transform Letter Spacing Word Spacing Text Shadow Text Wrap Variable Fonts Content Box Padding Box Border Box Margin Box Box Sizing Property Margin Padding Border Outline Box Shadow Block Display Inline Display Inline Block Display Static Position Relative Position Absolute Position Fixed Position Sticky Position Top Element Position Right Element Position Bottom Element Position Left Element Position Z Index Flexbox Box Layout Display Flex Flex Direction Flex Wrap Justify Content Align Items Align Content Gap, Row Gap & Column Gap Flex Grow Flex Shrink Flex Basis Flex Shorthand Order Property Align Self Practical Applications CSS Grid Layout Grid Display Grid Template Columns Grid Template Rows Grid Template Areas Justify Items Grid Auto Columns Justify Self Nested Grids Responsive Web Design Min Width Max Width Orientation Logical Operators Pointer Hover Prefers Color Scheme Fluid Images Flexible Typography Viewport Width Advanced CSS Features Defining variables Using variables Scope & Inheritance of CSS Variables Property Value Fallback Practical Applications :Hover :Active :Focus :Focus Visible :Visited :Link :First Child :Last Child :Nth Child :Nth of Type :Empty :Checked :Disabled :Enabled :Valid :Invalid :Required :Has :Not :Is :Where ::Before Pseudo Element ::After Pseudo Element ::First Letter ::First Line ::Selection ::Marker CSS 2D Transformations CSS 3D Transformations Transform Origin Transform Style Backface Visibility Transition Property Transition Duration Transition Timing Function Transition Delay Transition Shorthand Ease Timing Function Linear Timing Function Ease In Timing Function Ease Out Timing Function Ease In Out Timing Function Cubic Bezier Function Animations (@keyframes) Defining @keyframes Animation Name CSS Animation Duration Animation Timing Function CSS Animation Delay CSS Animation Iteration Count Animations Direction CSS Animation Fill Mode CSS Animation Play State CSS Filter Blur CSS Filter Brightness CSS Filter Contrast() CSS Drop Shadow CSS Grayscale CSS Hue Rotate CSS Invert CSS Opacity CSS Saturate CSS Sepia Mix Blend Mode Background Blend Mode Object Fit & Object Position Scroll Snap Type Scroll Snap Align Scroll Padding Scroll Margin Scroll Triggered Animations JS Variables

Scroll Triggered Animations

Scroll-triggered animations link the playback of a CSS animation to the user's scroll position. Instead of running on a timer, the animation scrubs forward or backward as the user scrolls up or down a container, offering a powerful way to create engaging and interactive web experiences. This modern CSS feature uses the animation-timeline property to bind an animation to the scroll progress of an element.

Example 1: Fade-in on Scroll

HTML

<div class="scroll-container">
  <div class="animated-element fade-in"></div>
</div>

CSS

/* Assigns a name to the scroll timeline */
.scroll-container {
  scroll-timeline-name: --fade-in-timeline;
  scroll-timeline-axis: block; /* Vertical scrolling */
  height: 200vh; /* Ensures there is scrollable area */
}

/* Links the animation to the scroll timeline */
.animated-element.fade-in {
  animation: fade-in-animation linear;
  animation-timeline: --fade-in-timeline;
}

/* Defines the keyframes for the fade-in effect */
@keyframes fade-in-animation {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

Explanation This example demonstrates a simple fade-in effect. As the user scrolls down the .scroll-container, the .animated-element gradually becomes visible, with its opacity directly tied to the scroll progress.

Example 2: Progress Bar

HTML

<div id="progress-bar"></div>
<div class="content"></div>

CSS

/* Creates a scroll timeline based on the entire document */
body {
  scroll-timeline-name: --page-scroll;
}

/* Styles the progress bar and links it to the page's scroll timeline */
#progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 5px;
  background-color: blue;
  animation: progress linear;
  animation-timeline: --page-scroll;
}

/* Defines the keyframes for the progress bar's width */
@keyframes progress {
  from { width: 0%; }
  to { width: 100%; }
}

.content {
  height: 2000px; /* Gives the page scrollable content */
}

Explanation This code creates a reading progress bar at the top of the page. The width of the #progress-bar expands from 0% to 100% as the user scrolls from the top to the bottom of the document.

Example 3: Rotate on Scroll

HTML

<div class="scroll-container">
    <img src="gear.svg" class="animated-element rotate">
</div>

CSS

.scroll-container {
  scroll-timeline-name: --rotate-timeline;
  height: 300vh;
}

/* Ties the rotation animation to the scroll timeline */
.animated-element.rotate {
  width: 100px;
  height: 100px;
  animation: rotate-animation linear;
  animation-timeline: --rotate-timeline;
}

/* Defines the keyframes for a full 360-degree rotation */
@keyframes rotate-animation {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

Explanation In this example, an image will complete a full 360-degree rotation as the user scrolls through the .scroll-container. The rotation progress is directly synchronized with the vertical scroll position.

Example 4: Scaling Up an Element

HTML

<div class="view-container">
  <div class="scale-up-box"></div>
</div>

CSS

/* Defines an animation timeline based on the element's visibility */
.scale-up-box {
  animation: scale-up-animation linear forwards; /* 'forwards' keeps the final state */
  animation-timeline: view();
  animation-range: entry 0% cover 50%; /* Animation runs as the box enters the viewport */
}

/* Keyframes to scale the element from small to large */
@keyframes scale-up-animation {
  from {
    transform: scale(0.5);
    opacity: 0.5;
  }
  to {
    transform: scale(1);
    opacity: 1;
  }
}
.view-container{
  height: 200vh;
  padding-top: 100vh; /* Pushes the box down to demonstrate entry */
}

Explanation Here, the .scale-up-box animates as it enters the viewport. The view() function creates a timeline based on the element's visibility, and animation-range specifies that the animation occurs as the element enters and covers the first 50% of the viewport.

Example 5: Horizontal Movement

HTML

<div class="scroll-container">
  <div class="animated-element move-horizontal"></div>
</div>

CSS

.scroll-container {
  scroll-timeline-name: --move-timeline;
  height: 250vh;
}

/* Links the horizontal movement animation to the scroll timeline */
.animated-element.move-horizontal {
  animation: move-animation linear;
  animation-timeline: --move-timeline;
}

/* Keyframes for moving the element from left to right */
@keyframes move-animation {
  from { transform: translateX(-100px); }
  to { transform: translateX(100px); }
}

Explanation This demonstrates moving an element horizontally based on vertical scroll progress. As you scroll down, the .move-horizontal element slides from left to right across the screen.

Example 6: Chaining Multiple Animations

HTML

<div class="scroll-container">
    <div class="animated-element multi-step"></div>
</div>

CSS

.scroll-container {
  scroll-timeline-name: --multi-step-timeline;
  height: 400vh;
}

.multi-step {
  animation: multi-step-animation linear;
  animation-timeline: --multi-step-timeline;
}

/* Keyframes with multiple steps for a complex animation sequence */
@keyframes multi-step-animation {
  0% { opacity: 0; transform: translateY(50px); }
  50% { opacity: 1; transform: translateY(0); background-color: blue; }
  100% { opacity: 0; transform: translateY(-50px); background-color: red; }
}

Explanation This example shows a multi-step animation where an element fades in, changes color, and then fades out as the user scrolls. The keyframe percentages correspond to the scroll completion within the container.

Example 7: Parallax Effect

HTML

<div class="parallax-container">
  <div class="background-layer"></div>
  <div class="foreground-text">Scroll Down</div>
</div>

CSS

.parallax-container {
  height: 150vh;
  position: relative;
  overflow: hidden;
  scroll-timeline-name: --parallax-timeline;
}

/* The background moves slower, creating a parallax effect */
.background-layer {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100vh;
  background-image: url('https://via.placeholder.com/800x600');
  background-size: cover;
  animation: parallax-scroll linear;
  animation-timeline: --parallax-timeline;
}

/* Keyframes to move the background vertically at a different rate */
@keyframes parallax-scroll {
  to {
    transform: translateY(50vh);
  }
}

Explanation A classic parallax effect is achieved by animating the background's position based on scroll. As the user scrolls, the background layer moves at a slower rate than the scroll speed, creating a sense of depth.