title: how to change the active-state background-color of buttons in Angular-Material?
body: <p>The title nearly asks all:<br><br>
  1. How can I change the color when the button was <strong>clicked</strong> ?<br>
  1. How can I change the color when the button is <strong>hovered</strong>?<br>
  <br>
  Angular-Material already provides a hover- and active-effect (with the same color and opacity); but I havn't found the place where I can change the default settings . . .<br></p>