Browser set monospace font is completely ignored by Github

[RaphGL]

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Despite having set the monospace in both Chromium and Firefox, the font is not set on the website. This is an accessibility problem as the default font set by GitHub makes it very hard for me to read the page without straining my eyes.
I've looked around and GitHub uses ui-monospace as their default, but changing it to monospace instead would allow people to override the monospace font in their browser settings as they see fit.

[devrose04]

Thank you

[Calc-oholic]

Isn't possible.

[RaphGL]

can u further elaborate what you mean here?

[khaledh]

Can we re-open this? What's the purpose of being in control of fonts used by the browser when websites just ignore them?

Aside: Does anyone know how to map ui-monospace in macOS to a different font? I believe it defaults to SF Mono, but I'd like to use JetBrains Mono instead.

[xPaw]

Yeah I've tried that already, but it breaks the selection cursor because of the bizzare hidden textarea system.

[ericwbailey]

@xPaw Can you link me to where this source code is located so I can inspect it? I want to make sure I'm working from the same source of truth that you are.

[xPaw]

https://github.com/ValveResourceFormat/ValveResourceFormat/blob/0bc42e65e11b524198f142a701fee75045ce21c6/ValveResourceFormat/Resource/ResourceTypes/ModelAnimation/AnimationDataChannel.cs

I've made textarea color visible, and it aligns up perfectly, so it doesn't seem to be a css issue.

[ericwbailey]

Thanks for that, it's really helpful.

I believe the double textarea is used to power performant tokenization effects, as well as a couple of other features. I'm also going to reach out to that team to see if what options are available.

It might take a little bit to get both that and the inspection done, but thank you for the speedy reply.

[khaledh]

The issue is that the cursor position is determined based on hard-coded font family (ui-monospace), size (12px), and line height (20x). I tracked it down to this file and function:

// https://github.githubassets.com/assets/app/assets/modules/react-code-view/utilities/lines.ts
 
export function determineProperOffsetWithDummyDiv(charOffset: number, lineRawText: string, tabSize: number) {
  const dummyDiv = document.createElement('div')
  dummyDiv.style.position = 'absolute'
  dummyDiv.style.visibility = 'hidden'
  dummyDiv.style.fontFamily = 'ui-monospace,SFMono-Regular,SF Mono,Menlo,Consolas,Liberation Mono,monospace'
  dummyDiv.style.fontSize = '12px'
  dummyDiv.style.lineHeight = '20px'
  dummyDiv.style.whiteSpace = 'pre'
  dummyDiv.style.tabSize = tabSize.toString()
  ...
}

which is used by this hook in:

// https://github.githubassets.com/assets/app/assets/modules/react-code-view/hooks/use-cursor-navigation.ts

useEffect(() => {
  ...
      setLeftOffsetWithCursorLocationUpdate(
        determineProperOffsetWithDummyDiv(endValues.offset, linesData[endValues.line]?.rawText ?? '', tabSize),
        endValues.offset,
      )
  ...
}, [linesData, tabSize, textSelection])

So overriding the code viewer with a font size other than 12px (and to a slight degree when using a different font family) will always result in mis-aligned cursor.

[cehfisher]

Hello @RaphGL - thank you for providing this feedback! We will file this with our Accessibility team so that it can be reviewed and will follow-up here with any additional questions or updates. We apologize for the delay in responding on this discussion board in the past and aim to improve our response time going forward. Thanks again!

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[cehfisher]

Just a quick note that we are still actively looking into this issue, so adding a comment to this thread before the stale bot closes it 😅