adding a close button for universes

src/main.ts

@@ -134,6 +134,10 @@ export class Editor {
   close_settings_button: HTMLButtonElement = document.getElementById(
     "close-settings-button"
   ) as HTMLButtonElement;
+  close_universes_button: HTMLButtonElement = document.getElementById(
+    "close-universes-button"
+  ) as HTMLButtonElement;
+
   universe_viewer: HTMLDivElement = document.getElementById(
     "universe-viewer"
   ) as HTMLDivElement;
@@ -494,6 +498,10 @@ export class Editor {
       editor?.classList.remove("invisible");
     });
 
+    this.close_universes_button.addEventListener("click", () => {
+			this.openBuffersModal();
+    });
+
     this.font_size_slider.addEventListener("input", () => {
       const new_value = this.font_size_slider.value;
       this.settings.font_size = parseInt(new_value);