Tangerine dark theme for Gitea

See also Customizing the look of Gitea

• Copy theme-tangerine-dream.css to $GITEA_PUBLIC/public/css
• Edit the [ui] section of app.ini
  • Add tangerine-dream to the THEMES setting. This setting should be a comma-separated list of the themes you want to be available on your setup (e.g. THEMES = gitea,tangerine-dream)
  • If you want to set this theme as default, add DEFAULT_THEME = tangerine-dream
• Restart gitea