[ticket/12292] Fix syntax error in admin.css

PHPBB3-12292
Merge remote-tracking branch 'VSEphpbb/ticket/12292' into develop-ascraeus

* VSEphpbb/ticket/12292:
  [ticket/12292] Fix syntax error in admin.css
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12292] Fix syntax error in admin.css