docs: Update multi-track examples with diverse cello, correct constraints, and model_dim=8

Author: DaoTwenty

docs/assets/extra.css

@@ -120,3 +120,100 @@
   background-color: #0a0c12;
   border-top: 1px solid rgba(255, 255, 255, 0.06);
 }
+
+/* ── MIDI Player & Visualizer (Slate/Red Theme) ─────────────── */
+midi-player {
+  display: block;
+  width: 100%;
+  background: #161b25;
+  color: #e2e8f0;
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  border-radius: 8px;
+  margin: 1rem 0 0.5rem 0;
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.2);
+}
+
+midi-player::part(control-panel) {
+  background: #161b25;
+  color: #e2e8f0;
+  border: none;
+  border-radius: 8px;
+  padding: 8px 16px;
+}
+
+midi-player::part(play-button) {
+  color: #eb1c3b;
+  background: rgba(235, 28, 59, 0.1);
+  border-radius: 50%;
+  padding: 4px;
+}
+
+midi-player::part(play-button):hover {
+  background: rgba(235, 28, 59, 0.2);
+}
+
+midi-player::part(time-text) {
+  font-family: 'JetBrains Mono', monospace;
+  font-size: 0.85rem;
+  color: #94a3b8;
+}
+
+midi-visualizer {
+  display: block;
+  width: 100%;
+  height: 150px;
+  background: #0a0c12;
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  border-radius: 8px;
+  margin-bottom: 1.5rem;
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.25);
+  overflow: hidden;
+}
+
+/* Customizing the visualizer canvas internally (piano-roll notes color) */
+midi-visualizer piano-roll-visualizer {
+  --piano-roll-background: #0a0c12;
+  --piano-roll-grid-color: rgba(255, 255, 255, 0.03);
+  --piano-roll-note-color: #eb1c3b;
+  --piano-roll-note-active-color: #ef4d63;
+}
+
+.midi-example-card {
+  background: #161b25;
+  border: 1px solid rgba(255, 255, 255, 0.06);
+  border-radius: 8px;
+  padding: 1.2rem;
+  margin: 1.5rem 0;
+}
+
+.midi-example-video {
+  display: block;
+  width: 100%;
+  aspect-ratio: 16 / 9;
+  background: #0a0c12;
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  border-radius: 6px;
+  margin: 0.8rem 0 0.7rem;
+}
+
+.midi-download-btn {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.5rem;
+  background-color: rgba(255, 255, 255, 0.06);
+  color: #e2e8f0;
+  padding: 0.4rem 0.8rem;
+  border-radius: 4px;
+  font-size: 0.8rem;
+  font-weight: 500;
+  text-decoration: none !important;
+  transition: background-color 0.2s, color 0.2s;
+  border: 1px solid rgba(255, 255, 255, 0.1);
+  margin-top: 0.5rem;
+}
+
+.midi-download-btn:hover {
+  background-color: var(--md-primary-fg-color);
+  color: #ffffff;
+  border-color: var(--md-primary-fg-color);
+}