Obs: this answer is only for WebKit, could not be found for other browsers and did not test them with names - .
The code:
Given that you have an element with the following CSS:
.styled { resize:both; overflow:auto; background:orange; }
If you add the pseudo-selector webkit ::-webkit-resizer , you can configure the handle:
::-webkit-resizer { border: 2px solid yellow; background: blue; box-shadow: 0 0 2px 5px red; outline: 2px dashed green; display:block; width: 150px !important; height: 150px !important; }
Visual:

http://jsfiddle.net/RaphaelDDL/ryphs/1/
Final thoughts
I tested with ::-moz-resizer on FF22, did not work. so yes, you are stuck in creating a javascript version by mimicking a descriptor for the StackOverflow text environment.
Additional Information
When modeling shadow pseudo-tag selectors, DO NOT add them to a single selector ::-webkit-resizer, ::-moz-resizer { /*css*/} , because this will invalidate the entire selector.
RaphaelDDL
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