You will NEVER style browser built-in tools the same across multiple browsers and across multiple OS.
I have been doing this a very long time and my best advise it to style as-best-as possible and reserve quirky css hacks for old IE browsers.
If you want to be super-anal about exact pixels, you need to not use the select html tag and instead use a ul tag. Then use css to list-style: none;
<ul id="my_selectbox">
<li>Option 1</li>
<li>Option 2</li>
</ul>
Then, style the menu to look exactly how you want it to look.
So think of this as a menu instead of a selectbox.
Then use javascript to make the menu drop down like a select tag.
(but that sure is a lot of work for a few pixels isn't it?)
Remember, you will NEVER EVER write a CSS file that makes all browsers look identical. Just isn't how they are designed. If you have a manager that demands it, they need to learn how this stuff works.
further note: you will have to also use javascript to store a selection. I can write you a quick script that does this if you need it. Not sure how proficient you are with javascript.