I have the following css-code:
.readMore:before { content: \'\'; display: block; float: left; width: 10px; height: 27px; margin: 0;
I just styled the height based on rem values, e.g. height: 2 rem. Can't confirm that's the best solution, but for responsiveness worked out quite perfectly in 1 line of code.
rem
height: 2 rem