Small issue, but maybe not worth spending too much effort to fix, given the low demographic it may affect:

Using firefox 68 ESR on Windows (at work), the text in the demo page looks like it's been strike-through, it is barely readable.

Each line of text has two horizontal lines (one pixel high each) filled with transparency...

Disabling the "Windows 65" font family solves the problem - but then Segoe UI is used.