You can look up the tab-pills definition within the lib folder (the .tab-pills.mx-tabcontainer part in _tabcontainer.scss), and copy this to the _tabcontainer.scss file in your custom folder, but then apply it to the 'standard' tab container styling. That should do the trick.
Cann't you add the tab-pills as class in your page definition?
Other option is to override the default tab container definition in your custom theme part (In file: styles/sass/custom/components/_tabcontainer.scss)