Fonts are changing sizes and look differently on mobile (Gmail) and Outlook (Web)

Fonts are changing sizes and look differently on mobile (Gmail) and Outlook (Web)

Is anybody having a problem where the text appears a different size on mobile devices than on Outlook? I finally got the email to display properly on PC's and then went on to do a final test on mobile before sending only to discover that half of the text is randomly in a bigger font. This is highly annoying as the email was ready to go, and now I have to go and fiddle around with it so that it will display correctly on mobile.

This isn't caused by copy and paste as this seems to happen no matter what way the text is input.