I threw together a darkened stylesheet that works with Stylish or something similarly Stylish-compatible. Whether or not this is something that can be changed server-side is another thing, but it looks alright. It shouldn't be too hard to change the colours yourself, either! Here it is!
I've tried to iron out glitches, but I doubt I've caught everything. Some white things will use white text and some dark things will use black text.
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