Bartik's main menu sub-links look ugly

[ghost]

The sub-links in Bartik's main menu look ugly. They are styled as 'tabs' but appear under the top-level tabs: ('Test 2' is a sub-menu item of 'Test')

I propose instead something like this:

Steps to reproduce:

• Set Bartik as the default theme
• Choose 'Rounded tabs' as the Main Menu Tab Style in the theme settings
• Edit the Default layout and set the Primary Navigation block to use 'Hierarchical tree' as the Menu Style
• Add a new menu item as a child of 'About' (e.g. posts/your-first-post)
• View the About page (about) to see the issue with the child menu item: