Add possibility to add a gradient background with fixes and fallbacks for various email-clients. Gradients are widely used in email design You always see some nice and clean emails with gradients sent by different brands. But it indeed requires a lot of fallbacks for Outlook, Yahoo, AOL, for example. Would be nice if you could add a gradient tab for background colors like in this guide, for example: https://www.litmus.com/blog/background-colors-html-email (or based on some fresher information). This gradient background tab could contain these fields:

1) RGBA CSS gradient

2) Two fallback colors for Outlook with VML gradients

3) Image gradient (a fallback for Outlook, Yahoo and AOL)

4) A solid fallback color for all other email clients

5) A partial fix for Gmail's dark mode: add a linear gradient to the background image CSS property using HEX colors

6) A further fix: Prevent text colors from being inverted in Gmail: https://www.hteumeuleu.com/2021/fixing-gmail-dark-mode-css-blend-modes/