How to reuse styles in Custom Template?

I'm adding a Custom Template to the Confirm Button, because I wanted to disable it before the user selects a Time.

The issue is, I'm having to clone all of the base styling from `.timepicker-button` and it doesn't seem good for maintainability.

Either that, or Importing the Button Component (I can see it is not currently exported) and customizing its `disabled` property somehow?