I humbly suggest Espresso 2.
From their website:
The one and only CSSEdit 3 — CSSEdit's award-winning visual tools, now
inside Espresso. With awesome CSS3 support for multi-browser
gradients, shadows and more.
Web Preview with X-ray — See how your CSS affects web layouts,
visualize margins and padding, and quickly find the relevant style
rules for any page element.
Powerful and Efficient Coding — CodeSense, code folding, smart
snippets, Zen coding and the drag-and-drop Navigator help you write
better code in less time.
Live Styling and Overrides — Edit any website's CSS and see it update
in real-time. No need to save, publish or reload. Experimenting and
tweaking has never been this fun.
Effortless Sync and Publishing — With Quick Publish, Server Sync and
Browse, you have the right tool for any server-based workflow. The new
Vroom engine is super-fast.
A Workspace That Fits Into Your Workflow — The innovative Workspace
gives you the flexibility of Tabs while integrating smoothly with your
Fantastic Find — Needle and haystack, meet Espresso. Project-wide Find
and Replace, Quick Filter and colorized regex make searching through
files or text a breeze.
Ruby, Python, Apache and Markdown. Or extend Espresso with XML/JS
You could read a review from Mac Appstorm to have an idea of the quality. They give it 10/10.