5 Powerful Web Platform Features You Probably Missed in 2025

Source: Dev.to

Overview

Below you’ll find a quick rundown of each feature, its browser support, core API details, and practical use‑cases.

1. moveBefore() — Finally, True DOM Movement

Support

• Chrome 133+
• Firefox 144+
• Safari (in development)

What it does

moveBefore() moves an element to a new location without destroying its state. Unlike appendChild() or insertBefore(), it preserves:

• Animation and transition progress
• Focus and active states
• Fullscreen mode
• Popover open/close state
• Modal state

Example

// Old way: state is destroyed
newParent.insertBefore(element, referenceNode);

// New way: state is preserved ✨
newParent.moveBefore(element, referenceNode);

if ('moveBefore' in Element.prototype) {
  mainContent.moveBefore(videoPlayer, null);
} else {
  // Fallback for older browsers
  mainContent.appendChild(videoPlayer);
}

Real‑world use case: Building a responsive layout where a video player moves from a sidebar to the main content area on mobile—without interrupting playback.

2. CSS Custom Highlight API — Highlighting Without DOM Surgery

Support

Baseline as of June 2025 (Chrome, Edge, Safari, Firefox 140+)

What it does

Define text ranges in JavaScript, style them in CSS, and keep the DOM untouched. This eliminates layout thrashing caused by inserting elements.

Example

// Find text and create a range
const range = new Range();
range.setStart(textNode, startIndex);
range.setEnd(textNode, endIndex);

// Register the highlight
const highlight = new Highlight(range);
CSS.highlights.set('search-result', highlight);

::highlight(search-result) {
  background-color: #fef08a;
  color: #1e1e1e;
}

Why it matters

• Zero DOM mutations → zero layout thrashing
• Multiple ranges can share one highlight name
• Highlights can span across element boundaries
• Ideal for search‑as‑you‑type UIs

Pro tip: A single Highlight object can hold multiple Range instances, so you can highlight all search matches with one CSS rule.

3. field-sizing: content — Auto‑Growing Form Fields in One Line

Support

• Chrome 123+
• Edge
• Safari 26.2+

What it does

Form controls automatically grow and shrink to fit their content, removing the need for JavaScript resize handlers.

Basic usage

textarea,
input,
select {
  field-sizing: content;
}

Constraining size

textarea {
  field-sizing: content;
  min-block-size: 3lh;   /* At least 3 lines */
  max-block-size: 12lh;  /* Cap at 12 lines */
}

input {
  field-sizing: content;
  min-inline-size: 10ch;
  max-inline-size: 40ch;
}

Works with

• <textarea>
• <input> (text, email, url, etc.)
• <select> (both dropdown and multi‑select)

Progressive enhancement: Browsers that don’t support the property simply show fixed‑size fields, so no JavaScript fallback is required.

4. sibling-index() and sibling-count() — CSS Finally Knows Position

Support

• Chrome 138+
• Firefox (in development)

What they do

• sibling-index() returns the zero‑based index of an element among its siblings.
• sibling-count() returns the total number of sibling elements.

Example: Staggered animations

.card {
  animation: fade-in 0.3s ease-out backwards;
  animation-delay: calc(sibling-index() * 100ms);
}

@keyframes fade-in {
  from { opacity: 0; transform: translateY(10px); }
}

Example: Equal‑width columns without knowing the count

.tab {
  width: calc(100% / sibling-count());
}

Creative use cases

• Staggered animations
• Dynamic color gradients across items
• Responsive grid layouts based on item count
• Circular positioning with trigonometry

/* Rainbow gradient across any number of items */
.item {
  --hue: calc(360 / sibling-count() * (sibling-index() - 1));
  background: hsl(var(--hue) 70% 60%);
}

5. CSS Anchor Positioning — Tooltips Without JavaScript

Support

• Chrome 125+
• Safari 26+
• Firefox (expected late 2025)

What it does

Positions an element relative to a named anchor, handling flipping when overflow would occur.

Basic usage

.trigger {
  anchor-name: --my-trigger;
}

.tooltip {
  position: fixed;
  position-anchor: --my-trigger;
  position-area: top;
}

Implicit anchoring (Chrome 133+)

<button popover>Hover me</button>
<div popover>I'm anchored automatically!</div>

[popover] {
  position-area: bottom span-left;
  margin: 0;
}

The browser automatically creates the relationship between the button and the popover, eliminating the need for anchor-name.

Which Should You Adopt First?

Start with field-sizing: content.

• Zero risk: Unsupported browsers fall back to normal fixed fields.
• Zero JavaScript: Remove auto‑resize handlers.
• Immediate UX win: Forms feel more responsive.
• One line of CSS: Lowest effort, highest impact.

After that, CSS Anchor Positioning offers a big win for any tooltip, dropdown, or popover UI.

Wrapping Up

The web platform is getting genuinely better at things we’ve been solving with JavaScript for years. State‑preserving moves, auto‑sizing fields, and declarative positioning aren’t just nice‑to‑haves—they’re more performant, more accessible, and more maintainable than their JS equivalents.

These features are shipping in stable browsers right now. No flags, no polyfills required (though fallbacks are smart for moveBefore() and the sibling functions).

What overlooked feature are you most excited to try? Let me know in the comments below.