The progressbar colors should be inverted/changed. Doesn't need much more information as this is just a UI improvement.

I've added additionally a border to the progressbar, it's not a must, but it looks better for me.

Info: The Clean theme in Moodle 3.6 looks well!

After basbrands told me to change it to use the Bootstrap component it looks like this:

Actual result

1. Use Boost or Classic Theme (Moodle 3.7 upwards)
2. Go to "Site Administration > Courses > Upload courses"
3. Upload a file using the "Drag and Drop" functionality
4. The progressbar should now appear and show the upload progress
5. Verify that it looks incorrect, as the colors are inverted

Expected result

1. Use Boost or Classic Theme (Moodle 3.7 upwards)
2. Go to "Site Administration > Courses > Upload courses"
3. Upload a file using the "Drag and Drop" functionality
4. The progressbar should now appear and show the upload progress
5. Verify that it looks fine.