style(site): white text on a deeper brand colour on button hover

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

site/assets/css/style.css

@@ -393,6 +393,21 @@ section[id] {
   }
 }
 
+/* Hover: white text on a deepened brand colour (≈5:1 contrast) — the bright
+   neon faces around it then stand out against the darker face. The dark and
+   ghost variants keep their own backgrounds. */
+.site-btn:not(.sb-dark):not(.sb-line):not(.sb-ghost):hover,
+.site-btn:not(.sb-dark):not(.sb-line):not(.sb-ghost):focus-visible,
+.gym-switch-btn:hover,
+.gym-switch-btn:focus-visible {
+  background: color-mix(in srgb, var(--fitme-accent) 50%, #000);
+  border-color: color-mix(in srgb, var(--fitme-accent) 50%, #000);
+  color: #fff;
+  text-shadow: 0 1px 2px rgba(0, 0, 0, .35);
+}
+.site-btn.sb-dark:hover,
+.site-btn.sb-line:hover { color: #fff; }
+
 /* ── Bootstrap Nav Overrides ───────────────────────────────────────────────── */
 .nav-link {
   font-weight: 700;