Show shadow/fill on html-slider-response

[ethan216]

Hi, I am trying to make it so that the slider scales rendered via the html-slider-response plugin will fill the track space between the thumb and the start of the slider track on the left, as is the case with the default HTML range input elements:

This appears to be possible based on the response from this thread, but I've been unable to figure out how. I've tried futzing with the ".jspsych-slider" sections in jspsych.css, but was not successful. For reference, I am using jsPsych version 6.3.1.

Any input would be much appreciated!