From https://once.com/writebook

app/javascript/controllers/fullscreen_controller.js

@@ -0,0 +1,19 @@
+import { Controller } from "@hotwired/stimulus"
+
+export default class extends Controller {
+  static targets = ["button"]
+
+  connect() {
+    if (!this.element.requestFullscreen) {
+      this.buttonTarget.remove()
+    }
+  }
+
+  toggle() {
+    if (!document.fullscreenElement) {
+      document.documentElement.requestFullscreen()
+    } else if (document.exitFullscreen) {
+      document.exitFullscreen()
+    }
+  }
+}