line-height: unit-less > em = %

Specifying CSS's line-height property using unit-less values, is much more flexible (with regard to cascade and inheritance) than using an em-value or a %-value.

by Lucas Krause

HTML

Hello,<br />world.
<hr />
<span style="font-size:1.5rem;">Hello,<br />world.</span>
<hr />
<span style="font-size:2rem;">Hello,<br />world.</span>

CSS

html {
    /**/
    line-height:1.5;
    /*/
    line-height:1.5em; /*or 150%* /
    /**/
}