You can use both a button and a with the buttons. A button is used for an action, an a tag for a link to (external) content.

Primary, purple button. Use with class yoast-button yoast-button--primary

Secondary, gray button. Use with class yoast-button yoast-button--secondary

Disabled secondary, gray button. Use with class yoast-button yoast-button--secondary

Upsell, yellow button. Use with class yoast-button yoast-button--buy

Upsell, yellow button with arrow. Use with class yoast-button yoast-button--buy and in the span use yoast-button--buy__caret

Small upsell, yellow button with arrow. Use with class yoast-button yoast-button--buy yoast-button--small and in the span use yoast-button--buy__caret

Remove button. Use with class yoast-remove

Hide button. Use with class yoast-hide

Close button