TestNG Emailable-report css lost after sending through Jenkins Gmail email notification

I am trying to send TestNG emailable-report.html result through Gmail after each build on Jenkins using

${FILE,path="directory_of_emailable_report.html"}

I set the Jenkins to trigger email send after each build. Somehow the emailable-report messed up like the css is not loaded as it is shown below:

Any idea on how to make gmail send the emailable-report as it is on the original html file?

Thank you