Update voice demo camera drawer

examples/webpage/styles.css

@@ -270,36 +270,29 @@ body {
   cursor: not-allowed;
 }
 
+/* 上传图片 + 使用摄像头 share one row. */
 .camera-drawer__sources {
   display: flex;
-  flex-direction: column;
   gap: 8px;
 }
 
-/* Mirror the mic controls: labeled device select + an action pill button. */
-.camera-drawer__camera-row {
-  display: flex;
-  align-items: flex-end;
-  gap: 8px;
-}
-
-.camera-drawer__camera-row .device-picker {
-  flex: 1 1 auto;
+/* The camera device dropdown only appears after "使用摄像头" is selected. */
+.camera-drawer__device-row {
   max-width: none;
 }
 
-.cam-btn {
-  flex-shrink: 0;
+.camera-drawer__device-row[hidden] {
+  display: none;
 }
 
-.cam-btn.is-active {
-  background: var(--success);
+/* Active state for the "使用摄像头" button once the camera is live. */
+.camera-drawer__source.is-active {
   border-color: var(--success);
-  color: #fff;
-  box-shadow: 0 0 0 6px rgba(45, 210, 139, 0.18);
+  color: var(--success);
 }
 
 .camera-drawer__source {
+  flex: 1 1 0;
   display: inline-flex;
   align-items: center;
   justify-content: center;