style: match step sequencer scrollbar styling

Author: britle20

src/features/drum-sequencer/DrumSequencer.module.css

@@ -58,6 +58,28 @@
   gap: var(--space-gutter);
   overflow-x: auto;
   padding: var(--space-panel);
+  scrollbar-color: var(--color-primary-container) var(--color-surface-container-lowest);
+  scrollbar-width: thin;
+}
+
+.sequencer::-webkit-scrollbar {
+  height: 10px;
+  width: 10px;
+}
+
+.sequencer::-webkit-scrollbar-track {
+  background: var(--color-surface-container-lowest);
+  border-top: 1px solid var(--color-outline-variant);
+}
+
+.sequencer::-webkit-scrollbar-thumb {
+  background: var(--color-primary-container);
+  border: 2px solid var(--color-surface-container-lowest);
+  border-radius: var(--radius-md);
+}
+
+.sequencer::-webkit-scrollbar-thumb:hover {
+  background: var(--color-primary);
 }
 
 .beatHeader,