Navigation
App Bar
A top bar built as a compound family: MAppBar owns layout integration and the scroll fill, while MAppBarNav, MAppBarTitle, and MAppBarActions place themselves. Size and alignment are independent axes, and a subtitle works on every size.App Bar
Describe the page, offer the essentials
An app bar orients people; it is not a container for every action.
Name the current page
Give the bar a clear title that matches where the person is, and keep trailing actions to the one or two that matter most here.
Do not overload the trailing region
More than two actions plus an overflow crowds the bar; move frequent page actions into a toolbar.
Keep the regions predictable
Leading is for navigation, trailing is for actions. Consistent placement lets people find controls without reading.
Leading = navigation
Use the leading slot for the menu or back control so it is always the first interactive element.
Match size to context
Reserve medium and large for pages whose identity deserves the extra height; interior pages usually read best as small.
Let scroll separate, not shadow
The bar communicates layering through a color fill on scroll.
Trust the fill
Keep the default scroll behavior so the bar separates from content the MD3 way, with a surface-container fill.
Do not add a drop shadow
Re-adding elevation on scroll reintroduces the M2 look and competes with the fill.