This is a unique styling feature of the Range Field. You can find it in the Range section of the Block Style settings tab. It helps you to set the width of the range. You can use pixels (PX) as the unit of measurement or choose to set the width as the percentage of the total column width. By default, it is set to 100%, so the range occupies the full width of the column to which you have put it.

setting width for the range field