It's not exactly what you're looking for, but if you download Cucumber's
QQUI Classic Velious Buff Window and unzip it into DuxaUI it will load properly and once you resize it it should be pretty close to what you're looking for. That's the best (only) way I know to get a classic-esque buff window into Duxa without editing XML.
Edit: If you want it to be transparent and with a titlebar
Open it in notepad
Ctrl + F
Search
<Screen item = "BuffWindow">
then scroll down to
<Style_Transparent>false</Style_Transparent>
Change false to true
then scroll down to
<Style_Titlebar>false</Style_Titlebar>
Change false to true and save it.
I just messed with it for a min, and that should get it really close to the Default as far as I can tell switching back and forth between them. If you follow that, it should look like this, but you can resize it however you want
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