can't resize the window that shows all the files

[Guest paulaE.]

somehow my files , say for photos, get completely expanded and takes u p the whole screen. I don't know how that happenedbut I can't get it back to the original size, smaller and in the left hand corner of the screen. The one that opens when you want to attach a file.I tried fixing it with the vertical double headed arrow at the sides but nothing happens. thanks

 

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