<center> isn't supported in Html 5, use <td align="center" style="text-align:center; display:table; table-layout:fixed;">.
If you don't use any CSS 3.0 features is pointless to use Html 5, better if you will use xHtml 1.0 Transitional.
You using attribute selector in your <styles>. Your email will be displayed in desktop view on mobile in Gmail app on Android and iOS.
Don't forget to validate your code.
You should remove the floating from you list. Floting isn't supported on Android devices from version 4.3.2 to 4.4.4, and that is almost 45% of Android market share.