Can anyone help with this?
Hard to debug and find the root problem without creating such app, first. I would guess that the Android default webview doesn't like a specific combination of attributes and values that you are using.
However, you might try that yourself: keep the .slink class as is, but remove the other parts. See if it shows your flat UI with proper font.
If it does, add the other classes step-by-step, until it fails. Then remove each attribute of the lastly added class one by one to find to 'bad' part.
Other process steps are feasible as well...the whole idea is to isolate the attribute combination that causes trouble.
(of course, I'm assuming that you haven't defined any of the css class definitions twice in your code, with conflicting attribute values; you should check that, though)
Alternatively, you could consider using the Crosswalk webview (you'd need the crosswalk plugin) and see if it works fine there.