I’ve run into this problem before
Setting the height of the select element works fine on webkit in Windows, but fails on webkit on a Mac.
If you set the css attribute
-webkit-appearance: menulist-button;
It will allow the height to work properly on a Mac, but it creates this weird black border on windows. You can adjust the border by setting the css border property, but that changes the look on all browsers that let you style select borders, not just webkit.
At this point, i gave up, but hopefully that is a good starting point if you want to investigate further.