Once a year I check the front-page of github https://github.com to see if they will ever fix their broken HTML. In short: They don’t.
You can check the HTML for instance by running the W3 validator like this:
https://validator.w3.org/nu/?doc=https%3A%2F%2Fgithub.com%2F
My journey started about three years ago. Due to my connections to the developer of Midori the light-weight browser, I constantly used that browser to find bugs. When visiting github.com the page just looked garbled. This occurs due to an error in their HTML.
This error is not only present once on the site, but also 400 lines later with the same introducing comment. Interestingly there are not starting tags for the closing of </textarea> and </xmp> present in the page. So it seems that the closing comment was shifted a bit in the wrong direction.
When writing to their support they told me to use Chrome (their most beloved supported browser) as it seems. They seem not to enjoy the web. Or standards. Or accessibility. Or their own code. That is sad. As usual I will write them an email.