Mike Krieger has ported the famous and elegant "Gmail Redesigned" stylesheet to Mailplane! Designed by GlobexDesigns, the stylesheet is part of the "Better Gmail" Firefox extension. It worked in Firefox only and thanks to Mike now in Mailplane, too.
Please visit the mailplaneapp Google group to get it. The CSS file is located in the "Files" section and is named "gmail-redesigned-webkit (n).css" (n is the version number).
Watch the installation screencast to get started:
Important: As the stylesheet is maintained by Mike, please post your suggestions, problems, and feedback to the mailplaneapp Google group.