This styling feature allows you to set the height of the Range Field’s range. That’s why you can meet it only in the Range section of that field’s Block Style tab. The height is defined in pixels and set to 5 by default. However, you can type into the bar the number from 1 to 20 or choose the value by moving the slider.
Here’s how the range looks like when the height is set to 1:
And now let’s change it to 20: