Q:

 dropdown a few pixels off

Consider this Bootstrap bug report. Basically, the <select> dropdown is not aligned with the <select> element on Chrome and Safari (both tested only a Mac). @mdo thinks there there is no fix. I just want a second opinion.
Can the <select> dropdown be aligned with the base <select> element?

A:

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.

