HTML template looks messed up in email which is sent by Maven

I am generating customized ATU Reports and sending them as HTML message file using Maven. But in email the report looks messed up and is not in proper format. The HTML template uses a CSS file for styling. Is there any way to get the report in proper format as mail?

This is POM.xml file for sending html report using maven postman plugin :

<htmlMessageFile> ${basedir}/ATU Reports/index.html </htmlMessageFile>