Syntax highlighting for code snippets on the lints website is broken

[Veetaha]

Go to the lints website, and you'll see how code examples are shown with almost the same color as the background. It's very hard to read them this way.

All the color themes are affected except it's a bit less critical with the light ones. However, code snippets still have no syntax highlighting with the light theme. They are displayed as monotone black text:

[y21]

Closing as a duplicate of #13536. This will be fixed by #13539.