24 20 16

Three sizes: 16 beside 15–17 px text, 20 in toolbars and buttons, 24 in empty states.
16 px is the floor. TYPO3.Icons are hinted for a 16-unit grid and optimised for that size — below it the shapes break down, and 18 or 22 land between grid lines. Use 16, 20, 24, or a whole multiple.

COLOUR

Icons are currentColor. Default is --text-secondary; --accent only on an active item; status colours only on status icons.

WITHOUT VISIBLE TEXT

answered version-bound — check the line the installation could not be booted boundary, stated on purpose

These may stand alone with a label. All other icons need visible text.

Run the checks Copy Read the tool surface Icon before a label, 8 px gap — except a direction icon, which follows it.