I have created a fiddle: http://jsfiddle.net/pQZ8f/
I want to have both the list items to be of same height without setting height manually. I want it to auto grow.
It's 2018, and we have display: flex, with 97.66% browser support (https://caniuse.com/#feat=flexbox)
With flexbox, all you need to do is:
ul { display: flex; } li{ width:100px; border: 1px solid black; }
Here's the fiddle: http://jsfiddle.net/pQZ8f/1076/