fix: 更新 Document Picture-in-Picture 占位符样式类名以提高可读性

packages/artplayer-plugin-document-pip/src/index.js

@@ -84,7 +84,7 @@ export default function artplayerPluginDocumentPip(userOptions = {}) {
         state.currentDoc = pipWin.document
 
         state.placeholder = document.createElement('div')
-        state.placeholder.className = 'artplayer-pip-placeholder'
+        state.placeholder.className = 'artplayer-document-pip-placeholder'
         state.placeholder.style.cssText = `display:flex;justify-content:center;align-items:center;width:100%;height:100%;`
         state.placeholder.textContent = options.placeholder
         state.originalParent = $container.parentNode

packages/artplayer-plugin-document-pip/src/style.less

@@ -1,4 +1,6 @@
-.art-video-player{
-    width: 100% !important;
-    height: 100% !important;
+.artplayer-document-pip {
+    .art-video-player{
+        width: 100% !important;
+        height: 100% !important;
+    }
 }