title: Set Angular HostBinding css class to value with function?
body: <p>I have a component that uses <code>@HostBinding</code> to set a class:</p>
  
  <p><code>@HostBinding('class.dark-1') true;</code></p>
  
  <p>Which works fine.  However, now I need to create a function in my component to change the class dynamically. </p>
  
  <p>For example, from <code>dark-1</code> to <code>light-2</code> when a button in the component is clicked.  </p>
  
  <p>I know how to create the function and call it from a button, but how do I change the class in the hostbinding and refresh the UI with the new class?</p>