You can copy over hexcodes, but otherwise importing styles isn't really a thing in the regular email editor.
Generally speaking, I advise most to construct a reusable template with the basic setup of how they want their emails to look - coloring, fonts, etc. - then copy each new email directly from that master template.
If you're wanting more customization with your email templates, including setting up stylings and coding in the formatting elements, I'd advise using the custom code editor.
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