Update javascript/app.js

javascript/app.js

@@ -121,7 +121,7 @@ class MidiVisualizer extends HTMLElement {
     this.shadowRoot.innerHTML = `
       <style>
         :host {
-          background-color: #your-color-here; /* Replace with your desired background color */
+          background-color: black; /* Replace with your desired background color */
           display: block;
           overflow: hidden;
         }