Set GMail message viewer and editor styles by label. e.g. mailing list messages that are best viewed with a monospace font.
Note: updated for the latest GMail as of 2020-05-11
Enables user to apply CSS to GMail message viewer and editor for selected labels only. Created for mailing list message viewing and editing that works best with monospace fonts but useful in many situations. Configuring CSS properties and one or more label names.
Can be used to increase font size in GMail editor without causing the email to be sent in the larger font or even rich text (HTML) format. Only affects your view of the message in the editor, not the recipient.