2004295 - anchored positioned element turns invisible when scrolling passed a point

Status: RESOLVED INVALID

(Core :: CSS Parsing and Computation, defect)

Description

[Nicolas Chevobbe [:nchevobbe]]

Attachment: anchor-positioning.html

Steps to reproduce

1. Open the attached test case
2. Scroll the page

Actual results

At some point, as the anchor gets scrolled away, the "This is an information box" element sticks to the top
Then if you keep scrolling, at some point the element vanishes (I'll post a screencast)
Its bounding client rect still report that it should be in the top left corner (DOMRect { x: 0, y: 0, width: 191.8000030517578, height: 162.39999389648438) , its computed display is still block, its visibility is still visible, there's no 0 opacity that would explain why you can't see it anymore

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Comment 1

[Nicolas Chevobbe [:nchevobbe]]

Attachment: screencast of the issue

Comment 2

[Timothy Nikkel (:tnikkel)]

Is this because position-visibility defaults to anchors-visible? I think I get your expected behaviour if I add position-visibility: always to the testcase.
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/position-visibility

Comment 3

[Timothy Nikkel (:tnikkel)]

(This testcase also displays quite differently in safari and chrome)

Comment 4

[Emilio Cobos Álvarez [:emilio]]

Yeah the visibility is expected.

Comment 5

[Nicolas Chevobbe [:nchevobbe]]

(In reply to Timothy Nikkel (:tnikkel) from comment #2)

Is this because position-visibility defaults to anchors-visible? I think I get your expected behaviour if I add position-visibility: always to the testcase.
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/position-visibility

Ah okay, I didn't know about this property and I was confused. I filed Bug 2004628 to surface it in DevTools

Comment 6

[Emilio Cobos Álvarez [:emilio]]

The visibility stuff seems invalid, the rest seems to be bug 1991929.