title: How to change background color of ngx-ui tooltip?
body: <p>I am using the following tooltip:</p>
  
  <p><a href="https://swimlane.github.io/ngx-ui/#tooltip" rel="nofollow noreferrer">https://swimlane.github.io/ngx-ui/#tooltip</a></p>
  
  <p>I want to make the background color green. How can I do this with the library?</p>