Cover: Use overflow: clip, falling back to overflow: hidden to allow sticky children (technically) #50237
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andrewserong
added
[Type] Bug
andrewserong
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noisysocks,
apeatling,
tellthemachines and
aaronrobertshaw
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Size Change: +25 B (0%) Total Size: 1.37 MB
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noisysocks
reviewed
May 2, 2023
noisysocks
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May 2, 2023
aaronrobertshaw
approved these changes
May 2, 2023
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Thanks for the reviews! |
andrewserong
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try/cover-block-use-overflow-clip-instead-of-overflow-hidden
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What?
Follow-up to #50209.
Add
overflow: cliprule to the Cover block's styling, falling back tooverflow: hidden.Why?
In #50209, the
overflow: hiddenrule was re-instated for the Cover block, so that rounded borders would correctly clip the inner background element. However,overflow: hiddencauses sticky positioned child elements to no longer be sticky to the overall document as it creates a new formatting context.overflow: clipon the other hand clips the overflow content without creating a new formatting context, so that sticky children can still scroll along with the document (while sticking to the parent container).Browser support appears to be pretty good amongst evergreen browsers (https://caniuse.com/?search=overflow%3Aclip), but to be on the safe side, I've preserved the fallback
overflow: hiddenfor older browsers.How?
overflow: cliprule to the Cover block, that overridesoverflow: hidden.overflow: hiddenis preserved so that the border radius still works correctly on older browsersTesting Instructions
Testing that this works correctly with sticky blocks is a little tricky — it involves creating a sticky group block outside of a Cover block, and then dragging it to be within the cover block. Then, add enough content to the cover block so that the sticky block is sticky when the window is scrolled. To make it easier, I've added some test markup below:
Test markup of a Cover block with a sticky group block within it
Screenshots or screencast
The below screengrab demonstrates that
overflow: clipallows both the cover block's background to be clipped and for sticky children to work correctly. Note that the UI for allowing non-root sticky position has not been enabled yet, as that is being worked on over in #493212023-05-02.15.37.16.mp4