Password generator app with JavaScript

Hi coders! Been a while since I used good old vanilla JS as I've been focussing very much on React for the last year. Decided to do a little bit of altering to the original design. I've set the minimum length input to 4 characters so the results can be: weak, medium or strong.

If anybody has a good idea on how to make the color of the slider 'inner-lane' to match the position of the slider-handle I'd love to hear it. Could not really make it work as I wanted.