To set a solid background color on text layers in your email design by selecting a Figma text layer in your email while the Settings panel is open, pasting in your hex color value (eg. #FFFBA8) into the Text Background Color input field. This will automatically add a solid background color behind that text content in your HTML email.

You can also optionally combine setting a background color on your text layer with adding inner padding to your text layer, which will provide some additional padding around the text content and give the background area some padding.