Update javascript/app.js

javascript/app.js

@@ -372,7 +372,7 @@ customElements.define('midi-visualizer', MidiVisualizer);
     divProgress.className = 'progressDiv';
     const rect = progressbarContainer.getBoundingClientRect();
     divProgress.style.width = rect.width + 'px';
-    divProgress.style.background = '#b4c0cc';
+    divProgress.style.background = 'black';
     divProgress.style.borderRadius = '8px';
     const divInner = document.createElement('div');
     divInner.className = 'progress';