Tabs manages which tab is active and positions the animated indicator. For the common underline pattern, pass TabsActiveIndicatorComponent={DefaultTabsActiveIndicator} and rely on the default TabComponent (DefaultTab). Use a custom TabComponent when you need layout or content beyond what DefaultTab provides. For pill / segmented controls, use SegmentedTabs instead.
Basics
Out of the box, Tabs uses DefaultTab for each row (headline text, optional DotCount via count / max on each tab) and DefaultTabsActiveIndicator for the animated underline. activeBackground sets the underline color (it is forwarded to the indicator as its background token).
You can omit TabComponent explicitly: Tabs defaults it to DefaultTab.
No initial selection
Dot counts
Optional count and max on each tab are forwarded to the badge next to the label (see DotCount).
Disabled
Disable the whole row with disabled, or set disabled: true on individual tab items.
Custom TabComponent
Use useTabsContext inside your own tab button.