title: how to get the minimum scroll thumb height in javascript
body: <p>I am trying to get the minimum height of the div scroll thumb in javascript,
  It looks like there is a minimum height that the browsers do not pass.
  in chrome it is 16 px.
  i need a formula to get it for all browsers
  i am able to get the height if greater or equal to the minimum 
  Can you help?</p>
  
  <p><a href="https://i.stack.imgur.com/A0NhD.png" rel="nofollow noreferrer">https://i.stack.imgur.com/A0NhD.png</a></p>