Fix theme on error pages
Description
https://gitlab.e.foundation/e/infra/backlog/-/issues/5316
some css variables were missing on guest.css or error pages don't have server.css, this is a fix
Screenshots
After change:
Technical details
Tests
Issues
https://gitlab.e.foundation/e/infra/backlog/-/issues/5316
10 commandments of code review
Edited by Alexandre Roux