Plugin for posting Code and Syntax

Hey all,

I’ve been having a hard time finding a simple plugin which will do what I need. I’m writing articles that involve showing programming code and need to highlight code blocks.

I’d like to be able to customize it, but essentially for code blocks, I need a gray background and fixed-width font. But I still need to be able to bold/italics/etc to highlight individual words within the code block.

Potentially something that lets me add it simply with a shortcode in the visual editor.

I would also be open to creating my own CSS, but I don’t know how to tie a shortcode in the visual editor to a particular CSS div or span (or some such). If someone has a link with a guide, I would greatly appreciate it!