Hi Colin
No, I select .zip files and extract them with a double-click - they remain .zip files until I do.
Hi Dave
It drags, but nothing happens - it just skips back to the SU window.
I had tried that, looking for a work-around 
So doing this doesn’t work?
Nope.
Not sure if this recording will work…
I wrote:
Sorry Dave - I didn’t read that carefully enough!
I never use thumbnails, as I prefer to see my description for styles
That works :-))
And the styles import into the other models!
Good one! Much obliged!
Still, there does seem to be a problem that will catch out other Mac users…
Good.
There was a thing a few years ago in which users couldn’t save out components by right clicking on them and choosing Save as … Dragging and dropping the thumbnail as I showed with styles did work however. I wonder if this is related.
I don’t know why it is but the thumbnail view for styles and components has always been required to do the drag and drop between panes thing.
Hi Dave
That’s a good memory you have 
What a bonus for us regular users to have you out there, jumping in to solve our myriad of issues.
As always, much appreciated!
Thank you. I can remember things like that but not what I had for breakfast this morning.
Dragging while in list view, or right-click save as when in list view, both work ok for me. So still something different about your system.
Hi Colin
I’m quite sure dragging in ‘list view’ used to work for me…
The thumbnails don’t do it for me, and I prefer ‘list view’, so am hopeful it’ll start working again.
I have no idea of the mechanism behind the operation, so couldn’t begin to fathom why it would work, then stop, and, in https://forums.sketchup.com/u/bmike’s case, suddenly start working again.
Your solution worked! (odd that it only works with thumbnail images, and not in list view.
Instructions for the confused (like me):
-
Enable the second Styles selection plane, click this button in the top right corner of the styles panel:
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Click this button in the top Styles selection area next to the collection name.
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Select “Small Thumnails” from the dropdown menu. If you don’t see this option, make sure you are on the top Styles selection area, not the bottom.
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Drag the thumbnail of the style you want, down the collection below. To create a new collection saved to your computer, click on the menu from step 2 and select “Create a new collection”.