That Snippet works like a charm. Thanks for sharing! I’m probably not going to use it, but good to have the option.
If you also want to change something like the font-size in the stack tabs mode make sure to add “.workspace-tabs.mod-stacked” in front, otherwise it will also change the look in the normal tab mode.
e.g.:
.workspace-tabs.mod-stacked .workspace-tab-header-inner-title {
text-orientation: upright;
font-size: 16px !important;
}