Plan step 36. <x-fab> renders data-md-fab with data-md-size,
data-md-color, data-md-variant, data-md-extended and, collapsing on
scroll, data-md-collapse-on-scroll with a bound data-md-collapsed; it
passes its glyph's size to <x-icon>. fab.css draws FabBaseline/Medium/
LargeTokens and ExtendedFab*Tokens per size, the container and filled
colours, elevation 3 and 4 on hover, the state layer and focus ring,
and the collapse morph that leaves actions.css.
data-fab becomes data-md-fab, also in navigation.css (the rail flattens
a nested FAB) and toolbar.css (a docked toolbar's FAB), with their tests.
The actions browser test gains the owed collapse-on-scroll test.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
