[Tails-dev] (review & merge request) CSS titles #6323

Hi

i integrated the modifications of esperal to the css and modified some
details too, see https://labs.riseup.net/code/issues/6323

[css-titles 4ea907a]
[css-titles b4fed49]
[css-titles 9a7d0cd]
[css-titles 47c112c]

on 451f repo, branch css-titles.

Please review & merge.
u.