2027 Web Platform Feature Ranking

Ranked proposals (top = most important)

1. CSS interpolate-⁠size property and calc-⁠size() function

   Allows animating to height: auto, and using intrinsic sizes in calculations.
2. JavaScript Temporal

   A modern and extensive date/time API to replace Date.
3. CSS container scroll-state queries

   The @container scroll-⁠state(...) at-rule applies styles based on the sticky positioning, snapped, and scrollable state of the container.
4. CSS anchored container queries

   @container anchored(fallback: …) applies styles based on which position fallback an anchor-positioned element is using.
5. Customizable/stylable <select>

   Customize the button, selected option, picker, and options with CSS.
6. HTML focusgroup attribute

   Combines descendant elements into a single tab stop, with arrow-key navigation between them.
7. Allow CSS transitioning/animating display and content-⁠visibility

   Useful for delaying display: none until an exit animation completes.
8. CSS gap decorations

   column-⁠rule and row-⁠rule display decorative lines between columns and rows of a flex, grid, or multi-column layout.
9. Interest invokers

   The interestfor attribute triggers actions on a target element when the user shows interest, such as via hover, focus, or long-press.
10. CSS corner-⁠shape property

    Alternative shapes for border-⁠radius, such as squircles and bevels.
11. HTML headingoffset and headingreset attributes

    Offsets the heading level of descendant <h1>–<h6> elements. Includes the CSS :heading() pseudo-class.
12. CSS reading-⁠flow and reading-⁠order properties

    Sets the order in which flex or grid elements are rendered to speech or reached via focus navigation.
13. CSS var() in size container queries

    Such as @container (width >= var(-⁠-⁠min-⁠width)).
14. Responsive iframes

    The frame-⁠sizing CSS property sizes an <iframe> to its content, avoiding scrolling within the iframe.
15. CSS margin-⁠trim

    Removes the margins of child elements when they meet the edges of the container.