Migrating buttons with custom elevations

This is also a relatively rare customization. Typically, only
ElevatedButtons (originally called RaisedButtons)
include elevation changes. For elevations that are proportional
to a baseline elevation (per the Material Design specification),
one can override all of them quite simply.

By default a disabled button’s elevation is 0, and the remaining
states are defined relative to a baseline of 2:

disabled:

hovered

or

focused:

baseline

pressed:

baseline

So to migrate a RaisedButton for which all elevations have been
defined:

RaisedButton

elevation:

focusElevation:

hoverElevation:

highlightElevation:

disabledElevation:

onPressed: