CSS - Formatting stacked tabs

Setup

Go to Settings, Appearance, and scroll all the way down to the CSS snippets section. You might already have some there, or not. It does not matter for us.

Click on the folder icon. This should open the local folder containing the snippets. Create a new file and give it a name that makes sense to you. For example, active tab color.css. Make sure that the file extension is css. If you don't see your file extensions, click on View, Show, and File name extensions (in Windows Explorer).

Now open the file and copy the CSS code below into it. Save the file, go back to Obsidian and refresh the list of snippets. Enable the active tab color one, and that should do it. If it does not, you may have to restart Obsidian.

Result

Using this snippet, you can easily change your active tab's appearance in terms of background color, outline color, font type, size, and font color.

Code

/* stacked tabs background color */
.workspace .mod-root .mod-stacked .workspace-tab-header-inner {
    background-color: rgb(224,224,224);
}

/* stacked tabs background color on hover */
.workspace .mod-root .workspace-tabs.mod-stacked .workspace-tab-container .workspace-tab-header {
     background-color: rgb(232,232,232);
}

/* stacked tabs - text orientation, font-weight, color */
.workspace .mod-root .workspace-tabs.mod-stacked .workspace-tab-container .workspace-tab-header-inner-title {
    text-orientation: upright;
    font-weight: 600;
    color: red;
}

Disclaimer

I found this on the Obsidian forum, posted by user ariehen on the Obsidian Forum.