I know about
<p>Then you should press <kbd>Enter</kbd> key or just press <ui>OK</ui> button.</p>
Is there a tag for user interface elements?
The appropriate element for marking up user input is
<kbd>element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands).
So your example would be appropriately marked up using:
<p>Then you should press <kbd>Enter</kbd> key or just press <kbd>OK</kbd> button.</p>