[ticket/13228] Fix codebox "select all" font-size in UCP and MCP

PHPBB3-13228
[ticket/13228] Gotta use !important after all. Too bad

PHPBB3-13228
Merge pull request #3160 from PayBas/ticket/13228

[ticket/13228] Fix codebox "select all" font-size in UCP and MCP
Merge branch 'develop-ascraeus' into develop