{"css":"","js":"","html":"<html>\n    <head>\n        <meta charset=utf-8>\n        <style type=\"text/css\">\n            div {\n                /*补全代码*/\n                width:4rem;\n                height:4rem;\n            }\n        </style>\n    </head>\n    <body>\n        <div></div>\n    </body>\n</html>","libs":[]}

em相对于父元素，rem相对于根元素。