Settings has a Theme row listing Settings.THEMES: Classic (main_theme.tres, still the default) and Original web (original_web_theme.tres), which looks like MusicFrontend: orange-bordered buttons, a #333 header and popups, #424242 panels, #4e4e4e alternating rows, a yellow playing song and a light grey player bar. Picking one sets the root window's theme at once and saves it as theme_id in settings.cfg, and it is applied at start. The popup backdrop and score graph follow a theme switch. The top bar has its own TopBarBackground style. test_theme.gd checks that every theme has everything main_theme.tres has. The screenshot tool takes a theme id. Closes #42 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>