Open Theme > Customize > Edit HTML
delete all codes.
Paste the codes below and save.
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html>
<html b:css='false' b:defaultwidgetversion='2' b:layoutsVersion='3' b:responsive='true' b:templateUrl='strm.xml' b:templateVersion='1.0.0' expr:dir='data:blog.languageDirection' expr:lang='data:blog.locale' xmlns='http://www.w3.org/1999/xhtml' xmlns:b='http://www.google.com/2005/gml/b' xmlns:data='http://www.google.com/2005/gml/data' xmlns:expr='http://www.google.com/2005/gml/expr'>
<head>
<b:skin><![CDATA[]]></b:skin>
</head>
<body>
<b:section class='main' id='main' showaddelement='no'/>
</body>
</html>