Slider marker not showing online

Issue: The slider marker only appears sporadically and very briefly in the online version of the study. I’ve tried both Chrome and Safari.

Study URL:

I realize this issue has been addressed several times in other posts. I have tried changing the color of the marker as suggested here. This didn’t solve the issue, and the marker shows up as red even though it should be white or gray.

I would be fine with either adding a requirement to press a key to continue (as suggested here) or delaying the start of the next video by a half second or so (as suggested here), as long as the participants are forced to provide a response before moving on. Unfortunately, I’m not savvy enough with JS to apply the solutions given in these posts to my own code. Many thanks in advance for any help!