LTSpice's GUI interface is left deliberately crude in order to allow it to function well and quickly under WINE (Allows Linux machines to run Windows code nativly) so it's not as polished as some more modernized and polished themes. Tweaking is required =)
I would personally love an overhaul of LTSpices user interface, but considering what it already does I'd rather they just stick to the basics of an extremely free powerful piece of software.