Mail / Calendar / Tasks etc. Can I change the text size of these titles in a Theme?

I am new to Em Client. The Title bars for the Mail, Calendar, Tasks, Contacts, etc. features are too big – they take too much real estate. This does not seem to vary between themes. Any hints as to where in the XML code for a theme to customize the font size and the size of these title bars? Is there a simpler way to reduce the size of these headings under Tools / Settings?

Don’t know about the Title and heading bars, but if you use the side by side arrangement you can simply resize the columns by hovering over the line until the horizontal double arrow appears.