style: 截图对比示例优化顶部占位 style

pages/webview-screenshot-comparison/webview-screenshot-comparison.uvue

 <template>
-  <view v-if="!isCustomNavigationBar" :style="placeholderStyle"></view>
+  <view v-if="!isCustomNavigationBar" class="top-placehoder"></view>
   <web-view id="webview-screenshot-comparison" class="webview-screenshot-comparison" :webview-styles="webviewStyles"
     :src="src" @loaded="loaded" @error="error">
   </web-view>
@@ -17,11 +17,6 @@
         isLoaded: false,
         statusBarHeight: state.statusBarHeight,
         isCustomNavigationBar: false,
-        placeholderStyle: {
-          display: 'block',
-          height: `${state.statusBarHeight}px`,
-          backgroundColor: '#007aff'
-        },
         devicePixelRatio: state.devicePixelRatio,
         webviewStyles: {
           progress: false
@@ -59,6 +54,10 @@
   }
 </script>
 <style>
+  .top-placehoder{
+    height: var(--status-bar-height);
+    background-color: #007aff;
+  }
   .webview-screenshot-comparison {
     flex: 1;
   }