[ticket/12498] Adds height-property for IE8 in tweaks.css

PHPBB3-12498
Merge remote-tracking branch 'Crizz0/ticket/12498' into develop-ascraeus

* Crizz0/ticket/12498:
  [ticket/12498] Adds height-property for IE8 in tweaks.css
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12498] Adds height-property for IE8 in tweaks.css