Rem sizing appears to be incorrect when used for container widths

Issue #23652919 • Assigned to Arvind M.


Sean ..
Oct 8, 2019
This issue is public.
Found in
  • Microsoft Edge
Found in build #
Reported by 3 people

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Steps to reproduce

Viewing the site
A max-width of 64 rems is applied to the page (base font size is set at 16px). This should result in a maximum page width of 1024px.

Chromium Edge is displaying this at 832px

Steps to produce

  1. Visit the URL
  2. Expand the viewport as wide as is possible on your device
  3. Observe that the width of the container does not extend passed 832px
  4. Observe that the left navigation bar scroll bar overlaps the main content

Expected behaviour

The container expands to a maximum width of 1024 at 1dpi and 16px base font.

Actual behaviour

The container only expands to 832px, subsequently the % values then appears to be calculated incorrectly.

The width of the navigation bar is 25% and the main content has a margin left of 25%. I’m aware the left navigation has a position fixed and this may be causing some of the issues?

Browsers tested in:
Chrome (latest stable)
Firefox (latest stable)
Edge (latest stable)
IE 11

Able to replicate in none of the above


Comments and activity

  • Chromium Edge seemingly ignores abolute font-size declaration in the body element for ALL rem-based font-size properties, not only for container-width.
    If calculates the rem-size from the font-size property of the html tag. If there isn’t an absolute font-size specified, Chromium Edge defaults all rem calculations on 13px.

  • Microsoft Edge Team

    Changed Assigned To to “Zachariah L.”

    Changed Assigned To to “Arvind M.”

  • set up a nested media query at 160px intervals that changed the content of a :before pseudoelement to reflect width stops. Set up another nested set at 8rem with root font-size set to 20px. This time the content of an ::after pseudoelement was set to change at the rem-based width stops.

    When sliding the window size, the ::before content was changing at 160 pixel intervals as set in the media query. These queries were behaving as expected from the px media stops. The ::after element was however changing roughly at the following stops: 253px, 128px, 130px, 127px, 130px, 127px, 127px… the intervals should have been a consistent 160px. Safari, Chrome and Firefox behave as expected.

    This issue breaks the correlation between rem media query lengths and lengths for background-image sizing, box sizing, font-sizing etc…

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