This is a helper addon for the Tree Style Tab 3.4.0 and later, and depends on the Tab Extra Contents API introduced at TST 3.4.0. If you use TST mainly for grouping tabs for each task, you may be suffered from too much collapsing/expanding trees on switching tasks. This helper addons provides small tab on a collapsed tree, it allows you to access the last active tab in the tree directly without expanding the tree. Please note that you need to use :part() pseudo element selector to apply your custom styling to the active tab indicator. For example: ---- ::part(extra-contents-by-tst-active-tab-in-collapsed-tree_piro_sakura_ne_jp tab) { background-color: red !important; } ---- Available part names can be inspected with the remote debugger for Tree Style Tab. (You need to run the debugger for Tree Style Tab, not for TST Active Tab in Collapsed Tree.)