OK. I even downloaded and installed the latest Beta 2.9.92 and the same thing? happened to me (Some of these are double clicks all left after the first one):
Right click on desktop-> Click on Settings tab at bottom right->Click on the Look button at top->Click on theme->Click on Basic theme[it has a checkmark next to it]->Click on Elive Light or Lucas since Dark is already chosen->Click Apply button
BOOM the bottom 20% of the dialog screen goes black and the mouse while movable can do nothing.
In less than a minute screen flashes and the "voice" says that "Elive desktop has initiated recovery"
BUT nothing has changed it's still the Dark theme.
SOLUTION: Before clicking the theme you want to change to: Click on the Basic button in the bottom right-> Choose your theme to change to->Click the apply button.
The screen flashes again but this time the theme you chose is now the theme.
I'll pass this to Samuel as well.
Good luck, Larry
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Linux User #305687
i5 3.35gHz 8GB RAM, NVIDIA GT218 [GeForce 210], 3 HDs (40 distros) - Elive Beta 2.9.90
Bradenton, FL EE.UU.