Use d-lh-{n} to change an element's line-height relatively. This means no unit is set with the line-height. Instead the line-height value is a multiple of the font-size.
Use d-lh{n} to fix an element's line-height. This allows you to target a specific line-height based on the font-size. For example if a target 20px line-height is desired and the current font-size is 14px, apply .d-lh6 to achieve this target (14px font-size + 6px = 20px target line-height).