After opening the guide, click "Add Step"
Step popup width and height options are present in image, message and inline step panels
By default the step popup width is 300 px and height is 100 px which is adjustable
The min/max popup width is 250 & 400 px and min/max popup height is 100 & 400 px
This scroller comes on the step if the description exceeds the default popup height
This is how the step looks when popup width and height are at maximum