Gradients and transparency are mostly used on the background of a palette but you can pretty much use them anywhere.
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A hoverable header is when you hover over it, it changes. At least I think thats what your referring too XD. I have one on my palette right now!
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I have a lot of borders removed on my palette right now as well. There just isnt black outline on all the different boxes, and in chat.
I dont have any drop shadows but its where the shadows are visible below the element you apply it to.
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I have the transparent text on my palette as well.
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Hope that helps with examples and I tried to answer your questions XD