<style>
    input { -webkit-appearance: none; background: silver; height: 20px; width: 200px; }
    input::-webkit-slider-thumb { -webkit-appearance: none; background: green; width: 10px; height: 50%; }
</style>
<p>The slider thumb below has a height specified as 50%. It should be a 10 pixel square.</p>
<input type="range">