This style will work for both horizontal & vertical tabs.
/**
* Tabs Plugin
* From Will-Myers.com
* Tab Underlines
**/
div.wm-tabs {
--nav-scrollbar-display: none;
--tabs-header-border-bottom-width: 0px;
--tab-button-active-background: transparent;
--tab-button-active-color: ~'hsla(var(--wm-accent-hsl), 1)';
--tab-indicator-track-size: 4px;
--tab-indicator-track-background: ~'hsla(var(--wm-text-hsl), 0.15)';
--active-indicator-size: 4px;
--active-indicator-border-radius: 0px;
}