Dialog/Drawer: lock scroll on the root element to prevent layout shift#42545
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Apply the dialog-open scroll-lock (overflow: hidden) to the root <html> element instead of <body>, so it sits on the same element as scrollbar-gutter: stable. Co-locating them keeps the gutter reserved while the scrollbar is hidden, so the page no longer shifts (and the ::backdrop covers the gutter instead of leaving a white strip) when a dialog or drawer opens. Fixes #39221, #39972, #40908, #40659.
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Pull request overview
This PR changes how Bootstrap 6’s Dialog/Drawer scroll-lock is applied so it targets the root (<html>) element instead of <body>, preventing layout shifts and “white gutter” artifacts when scrollbar-gutter: stable is used on :root.
Changes:
- Toggle the
dialog-openclass ondocument.documentElement(root element) instead ofdocument.body. - Update Dialog styles to scope scroll-lock to
:root.dialog-open. - Adjust unit tests and the v6 migration note to reflect the root-element scroll lock (and bump bundlewatch thresholds).
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
js/src/dialog-base.js |
Moves dialog-open toggling from <body> to <html> for correct scroll-lock behavior with scrollbar-gutter. |
scss/_dialog.scss |
Changes scroll-lock selector from .dialog-open to :root.dialog-open. |
js/tests/unit/dialog.spec.js |
Updates expectations/cleanup to check root element for dialog-open. |
js/tests/unit/drawer.spec.js |
Updates expectations/cleanup to check root element for dialog-open. |
site/src/content/docs/guides/migration.mdx |
Updates migration guidance to document root-element scroll prevention. |
.bundlewatch.config.json |
Adjusts bundle size budgets in anticipation of output changes. |
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| if (preventBodyScroll) { | ||
| document.body.classList.add(CLASS_NAME_OPEN) | ||
| // Lock scroll on the root element (not <body>) so it lands on the same | ||
| // element that carries `scrollbar-gutter: stable`. Co-locating them keeps | ||
| // the gutter reserved while the scrollbar is hidden, so the page doesn't | ||
| // shift (and the ::backdrop covers the gutter instead of leaving a strip). | ||
| document.documentElement.classList.add(CLASS_NAME_OPEN) | ||
| } |
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| @layer components { | ||
| // Prevent body scroll when dialog is open | ||
| .dialog-open { | ||
| // Prevent page scroll when a dialog is open. Applied to the root element so | ||
| // `overflow: hidden` sits on the same element as `scrollbar-gutter: stable` | ||
| // (see _root.scss): the gutter stays reserved while the scrollbar is hidden, | ||
| // so the page doesn't shift when a dialog opens. | ||
| :root.dialog-open { | ||
| overflow: hidden; | ||
| } |
This was referenced Jun 27, 2026
mdo
added a commit
that referenced
this pull request
Jun 27, 2026
…42575) * Tests: assert dialog-open on documentElement in dispose-while-open specs The dispose-while-open specs added in #42544 asserted the scroll-lock class on document.body, but #42545 moved the lock to the root element (documentElement). The two changes were each green in isolation but broke once both landed on v6-dev. Align these specs with the rest of the suite, which already asserts on documentElement. * Build: bump bundlewatch thresholds for cumulative JS growth on v6-dev bootstrap.bundle.js (83.15KB) and bootstrap.js (54.39KB) now exceed the prior thresholds after the dialog/drawer/tooltip/popover/menu fixes landed; each PR bumped only relative to its own base.
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Problem
Opening a dialog/drawer can shift page content sideways, and with
scrollbar-gutter: stablethe reserved gutter renders as a bare white strip instead of the dimmed overlay (#40659).Cause
scrollbar-gutter: stableis on:root(_root.scss), so the viewport scrollbar and its reserved gutter live on<html>. But the scroll-lock appliedoverflow: hiddento<body>. Because<html>'s overflow isvisible, the body→viewport overflow-propagation quirk hides the scrollbar at the viewport level while the gutter reservation stays on<html>— and in that split state browsers don't reliably honor the gutter, so content reflows and the gutter strip falls outside the native::backdrop.Fix
Apply the
dialog-openlock to the root element (<html>), co-locatingoverflow: hiddenwithscrollbar-gutter: stable. The gutter stays reserved while the scrollbar hides (no shift), and since<html>is the viewport scroller the::backdropcovers the gutter (no white strip).dialog-base.js: toggledialog-openondocument.documentElementinstead ofdocument.body._dialog.scss: scope the rule to:root.dialog-open.Fixes #39221, fixes #39972, fixes #40908, fixes #40659.