Buttons trigger an action or navigation. Choose the type by how much emphasis the action needs.
Sizes run from extra small to extra large:
Use one primary button per screen for the main action. Use secondary for alternatives and tertiary or link for low-emphasis actions. Use the destructive intent only for actions that delete or can't be undone.
Buttons can be reached and activated with the keyboard (Tab, then Enter or Space) and show a visible . Give icon-only buttons an accessible label.
Pending.