Those fonts probably aren’t available (by default) on Linux because they have proprietary licences.
(Not that it’s likely to be the root of the problem of course.)
It’s a bit of effort but I’d advise reworking the layout to use CSS flexbox.
I’ve dabbled in making my own website and found it’s a lot easier than messing around with things like float and z-index.
There’s a pretty good explanation of the various aspects of it here: