[Plugin: Tabber Tabs Widget] how to fix height and add scrollbar

i have this plugin installed and love it. my site has an incredible number of categories and i would like to give the tabber tab a fixed height and have the scroll bar show up. there are notes in the CSS file about doing this, but I can’t seem to figure it out. if someone would be kind enough to walk me through the steps? i am using style 2. thank you so much.

https://www.ads-software.com/extend/plugins/tabber-tabs-widget/