Custom Blogger template developers feel the need to make their templates more flexible in terms of custom assets, design responsivenes and increase blogger loading speeds but often experience problems due to the Widget CSS bundle file. Here is a simple hack to remove widget css bundles from blogger.
Step1: Before trying to do anything with the template, kindly take a backup to avoid the fate of broken templates. Check this - How to Backup/Restore/Change Blogger Templates?
Step 2: Press Ctrl+F and find this line -
<b:skin><![CDATA[...]]></b:skin>(... represents bunch-of-code in Blogger template)
Step 3: Replace it with this line -
<style type="text/css"><!-- /*<b:skin>*/</b:skin>Step 4: Again press Ctrl+F and find this line
<b:template-skin>... </b:template-skin>(... represents bunch-of-code in Blogger template)
Step 5: Replace it with this line -
<link href='https://www.yourhost.com/yourstylesheet.css' rel='stylesheet' type='text/css'/>(or)