Skip to content
Hypermedia Components

Browser support

Every component page carries its own Browser baseline table. This page states the policy those tables follow, so a fleet that is stuck somewhere — an iPad that will never see the next iPadOS, a Mac on an older macOS, a Firefox ESR — can be judged once.

The floor

Section titled “The floor”

The kit’s floor is the Popover API: popover, popovertarget and the toggle / beforetoggle events — Baseline 2024 (Chromium 114, Firefox 125, Safari 17). Menus, menubars, popovers, tooltips, hovercards, comboboxes and the filter bar are built on it, and there is no fallback for it: below the floor those surfaces do not open. Everything else the kit relies on unconditionally — <dialog>, :has(), @layer, dvh units, :user-invalid, requestSubmit(), the formdata event — is older than that.

A consumer whose fleet sits below the floor can load @oddbird/popover-polyfill before the behaviors bundle; the kit does not bundle it.

Above the floor

Section titled “Above the floor”

Features newer than the floor fall into three groups. The rule that sorts them: a functional loss gets a scripted, feature-detected, self-retiring fallback; a cosmetic loss gets none.

Scripted fallbacks

Section titled “Scripted fallbacks”
Feature Baseline Fallback Retires when
CSS Anchor Positioning (position-area, position-try-fallbacks) 2026 — Chromium 125, Safari 26, Firefox 147 anchor-fallback.js, shared by the eight floating behaviors: places the surface by script, flips on overflow, tracks scroll / resize CSS.supports('anchor-name', '--x') is true
Invoker commands (commandfor + command="show-modal" / "close") 2025 — Chromium 135, Firefox 144, Safari 26 installInvokerCommands(): one delegated click listener performs the two commands the kit blesses on a <dialog> commandForElement exists on HTMLButtonElement.prototype

Both are proved on every CI leg: the native path on the engines the suite bundles, and the fallback path by removing the API from the page before the bundle loads (invoker-commands-fallback.spec.mjs) or stubbing CSS.supports (the anchor specs).

Cosmetic degradations — no fallback

Section titled “Cosmetic degradations — no fallback”
Feature Baseline Without it
@starting-style + transition-behavior: allow-discrete (dialog, drawer) 2024 The surface snaps into place instead of sliding.
interpolate-size (accordion, collapsible) Chromium only Open / close is instant, not animated.
field-sizing: content (data-autosize textarea) Chromium 123, current Firefox and WebKit The textarea keeps its rows height and the resize handle.
scrollbar-width / scrollbar-color (scroll area, tabs, chat) 2025 Default scrollbars.
<details name="…"> (accordion) Chromium 120, Firefox 130, Safari 17.2 Panels are not mutually exclusive.
hidden="until-found" (tabs) Chromium 102 Inactive panels are plain hidden; find-in-page does not reveal them.
appearance: base-select (select) Chromium 135 The native picker — the kit styles nothing there yet.

Deliberately avoided

Section titled “Deliberately avoided”
Feature Why
popover="hint" Tooltips and hovercards use popover="manual" plus script: hint was still missing from Safari in 2026 and an unknown value degrades to manual anyway, so the kit writes what every engine at the floor reads.
CommandEvent, custom -- commands The kit needs two built-in commands; the fallback covers exactly those. Load invokers-polyfill for the full API.

What this means for a fleet

Section titled “What this means for a fleet”
  • Safari 17 / 18 (a Mac on Ventura, an iPad that stops at iPadOS 18): everything works; dialogs open through the invoker fallback, floating surfaces are placed by the anchor fallback.
  • Firefox ESR 140: the same two fallbacks are active; ESR 128 is at the floor as well.
  • Safari 16 and older, Firefox 124 and older: below the floor — load the popover polyfill or keep those users on a server-rendered path.

The per-component tables stay authoritative for exact versions; this page is the policy they implement.

Section titled “Related”