fix(fonts): wait for required fonts before displaying page content

web/demo.html

@@ -1,5 +1,5 @@
 <!doctype html>
-<html lang="zh-CN">
+<html lang="zh-CN" data-rm-fonts="loading">
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />