feat: theme more stuff and fix classes

[FedeIlLeone]

• Themed:
  • Soundboard popout.
  • Overwrite/add permissions popout.
  • Linked roles modal.
  • Server guide to do's.
  • Main buttons and icon in stage channels.
  • chatbox now covers split screen channels.
  • Hover payment history in billing user settings.
  • Disabled icon in overlay user settings.
• Fixed classes for forums, invite modal footer and app directory modal.
• Fixed hover in automod number input.
• Removed gray gradient in onboarding.
• Removed server boost page theme (everything changed since last time, lgtm as it is).