v3: tracked down many visual inconsistencies, added two new themes

src/themes/smooth.css

@@ -7,7 +7,12 @@
 /* ── Dark variant (default) ───────────────────────────────────────── */
 :root,
 :root[data-style="smooth"] {
-  font-family: "Saira", sans-serif;
+  /* Global font defaults — other themes override --font-body; App.css styles
+     consume these variables rather than hard-coding font names. */
+  --font-body: "Saira", sans-serif;
+  --font-mono: monospace;
+
+  font-family: var(--font-body);
   font-optical-sizing: auto;
   font-weight: 400;
   font-style: normal;
@@ -56,13 +61,16 @@
   --color-option-bg: #0d2340;
   --color-option-border: #001427;
 
-  /* Service brand colors (fixed, not theme-dependent) */
+  /* Service brand colors (fixed, not theme-dependent). `on-brand` is the
+     foreground for text sitting on any of these — also fixed, so the contrast
+     never flips with the theme's text colour. */
   --color-youtube: #c00;
   --color-youtube-hover: #f00;
   --color-bandcamp: #1da0c3;
   --color-bandcamp-hover: #25c8f0;
   --color-soundcloud: #f50;
   --color-soundcloud-hover: #f73;
+  --color-on-brand: #fff;
 }
 
 /* ── Light via system preference (auto color-scheme) ──────────────── */