A Dark theme that is suitable for what I do. to use efficiently, install and run lxappearance, and set GTK theme to "Inhuman". Then all what's left are (rare but annoying) white-background-colored form fields in web pages, but that's only the fault of stupid web "designers".

When that happens, fire up "firebug" (extension to both FFox & Chromium) : right-click on the offending white field, "inspect element" then in the element's CSS properties list, uncheck "background" voilà : You can type in an unslyled background, like God's intended it to be.