They have basically no css on that site. You should be seeing the default font of your browser. However, if you are browsing in dark mode you should see these colors and a text-shadow:
Another option is to use something like ws-butler[0], which only deletes trailing whitespace on lines you've edited. This way you don't create spurious diffs on version controlled files, which confuse code reviewers and `git blame` users in the future.
This is an awesome mode. I enabled it once and then just left it in there and it quietly does its thing. I really miss it in other editors.
(Of course, $employer enforces whitespace style globally with a linter so the files here can't end up in a state where ws-butler is meaningful. Not sure what I prefer.)
The one issue with this is for things like markdown where a code block is space-indented - if you want an empty line as part of the code block rather than two code blocks then you need a line that contains -only- the indentation.
I would expect that emacs being emacs it's trivial to configure such lines to be left alone when relevant, but it's worth remembering that the edge case exists.
Replace show-trailing-whitespace with automatically-deleting-whitespace, though.