Office 365 Email Signature Using Html And Css

Hi

Just wondering if anyone knows a work round office 365 email signature

We've had a new html signature designed by our web designers, it's html and css?? We copy and paste the html into the signature part of office 365 mail. Sending to a computer works fine however it doesn't format on the mobile devices??

I'm totally out of my depth here the people who designed it have said it's because 365 doesn't support the CSS code and that's the part that changed sizes on devices rec

Any help appreciated