This is the best thing I've found so far: http://www.seabreezecomputers.com/tips/find_custom2.js
(code to insert in your HTML is included in the intro section).
You can modify the styling of the pop-up box to match your CSS (default colors are rough). I made mine straight up gray: Modified JS is here: http://www.nextgenresale.com/wp-content/themes/TheCorporation/js/find_in_page.js
Main Drawbacks I've found:
-In Firefox, it disables the Control-F keyboard command
-Because it uses floating divs, sometimes when you hit next, the find on page window disappears from view. Confusing. But this only happens sometimes.
Overall: Better than nothing, but not a great solution.
Interesting: It has an option for Firefox only to trigger the native browser Control-F function! This is perfect, if only it didn't a) disable the actual keyboard Control-F command in Firefox, and b) if this also triggered the native Control-F find function in other browsers.