frontend: prepare for responsive font-size

[thisconnect]

In order to change the CSS to change the codebase to use rem, using 'The 62.5% Font Size Trick' we need to first convert all existing rem units back to px. This is so that we don't accidentally already have rem values.

If the default base font size is 16px, 1rem equals 16px. Changing back to pixel first makes it much easier to use the 62.5% trick where 1rem = 10px.

This refactoring should not introduce any visual change and just converted rem to px. I.e. 1.5rem is now 24px as 1rem currently equals 16px.

Also simplified terms.module.css a bit as the title was defined multiple times.