problem with the markers on the preview monitor

Hi,

I can't get rid of the markers on the preview monitor.

When I'm editing a video, I can see all the tracks.

On the first frame of the clip, a bar with a yellow corner appears on the left side.

On the last frame, a purple bar appears on the right side. I'd like to know how to get rid of them.

I've attached screenshots.

Thank you in advance for your help.

Best regards,
Krystian