[UI] Bug: footer height incorrect when screen-width to small

[EpicCoder]

• Gitea version (or commit ref): 5f4a40c
• Git version: Not relevant
• Operating system: Not relevant
• Database (use [x]): Not relevant
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL) https://try.gitea.io/
  • No
  • Not relevant
• Log gist:

Description

When use "arc-green" theme and the screen-width is too small then the footer hight is incorrect. It happens in both themes "gitea" and "arc-green" but in "gitea" theme you can't see it, because the body and footer background color are the same.

Screenshots