You might need to know about the CSS lh unit

The CSS `lh` unit equals the computed value of the `line-height` property and enables several practical layout techniques. Use cases covered include: setting paragraph margins proportional to line height, creating paper-line background effects that stay aligned when font size changes, rounding floated image heights to the nearest text line using `calc-size()` and `round()`, limiting list height to an exact number of lines with a matching fade mask, and sizing button icons relative to text. The unit solves problems that previously required pixel hacks or were difficult to maintain across font size changes.