Feature Request to Relative value for Line Height (like in css)

Hello,
I find it hard to experiment with font sizes because every change of size I need to manually adapt the line-height.
It is very strange that for software that wants to mimic html5 rendering, no relative (to the font-size) value can be entered. This very forum has line-height: 1.5, that means a line-height 1.5 times larger than whatever value is given for the font-size.

Thank  you!