Ken
I am also seeing this - Windows 10. Both the search field text and the preference/options tabs - text matches background colors.
@conema I incorporated your changes into my local install. The Option tabs and search text are now visible in the monterail theme.
For the tab shapes, I played around with adding the following lines to .tabmail-tab .tab-content classes: border-top-left-radius: 15px; border-top-right-radius: 15px; I found these suggestions on this website: https://css-tricks.com/better-tabs-with-round-out-borders/