How to create an image comparison slider with CSS?

clip-path defines a visible region for the slider’s top image, enabling responsive image comparison by clipping away unwanted parts; use inset() or percentage-based polygon() to avoid resize issues and ensure cross-browser compatibility.

What clip-path does for the slider handle

The core of a CSS-only image comparison slider is hiding part of one image while revealing the other — and clip-path makes that possible without JavaScript. It lets you define a visible region (e.g., a rectangle from the left edge up to a specific x-coordinate), and anything outside that shape is clipped away. You apply it to the top (overlay) image, then animate or adjust its value based on user interaction.

Common pitfalls:

• Using clip-path: polygon() with absolute pixel values breaks on resize — always prefer inset(0 0 0 X%) or polygon(0 0, X% 0, X% 100%, 0 100%) for responsive behavior
• clip-path doesn’t work in old Edge (
• Animating clip-path directly can jank; use will-change: clip-path sparingly, or prefer transform-based alternatives if performance matters

How to make the handle draggable with pure CSS

You can’t make something truly draggable using only CSS — but you *can* simulate it with a range input (<input type="range">) styled to look like a handle. The slider’s value drives the clip-path position via CSS custom properties.

Key steps:

• Wrap both images in a container with position: relative
• Stack the “before” image as background or bottom layer, “after” image on top with clip-path
• Use :root or a parent class to set a CSS variable like --clip-x: 50%, then bind it in clip-path: inset(0 calc(100% - var(--clip-x)) 0 0) (or equivalent polygon)
• Connect the <input>’s oninput to update --clip-x — this part requires one line of JS, but it’s minimal and unobtrusive

No pure-CSS drag means no mousemove or touchmove handling — if you need those, you’re already in JS territory.

Why background-image is safer than <img alt="How to create an image comparison slider with CSS?" > for the base layer

When the “before” image sits underneath the clipped “after” image, using background-image on a pseudo-element (::before) or div gives more control over sizing, positioning, and responsiveness — especially when you need background-size: cover or object-fit-like behavior without extra wrappers.

Compared to <img alt="How to create an image comparison slider with CSS?" >:

• <img alt="How to create an image comparison slider with CSS?" > respects max-width: 100% but may distort if height isn’t constrained; background-image ignores intrinsic aspect ratio unless you add padding-top tricks
• <img alt="How to create an image comparison slider with CSS?" > supports loading="lazy" and decoding="async"; background images don’t — so use <img alt="How to create an image comparison slider with CSS?" > if LCP matters
• If you need alt text or SEO image context, <img alt="How to create an image comparison slider with CSS?" > is mandatory — fallback to background-image only for decorative or secondary layers

Dealing with touch devices and focus management

The range input works on touch, but default iOS/Android styling hides the track and thumb — users might not realize it’s interactive. You must style input[type="range"] deeply: override ::-webkit-slider-thumb, ::-webkit-slider-runnable-track, and their Firefox/Edge equivalents.

Also:

• Add tabindex="0" to the container if you want keyboard support — otherwise, screen readers and keyboard users skip it
• Don’t rely on :hover alone for visual feedback; pair it with :focus-within or :focus-visible
• On iOS, the range input emits change only after release — use input event instead to get live updates

The hardest part isn’t the slider logic — it’s making sure someone on an old iPad, a keyboard-only user, or a screen reader gets the same clear, operable experience as a mouse user on Chrome.

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