Thank you for your feedback!
Currently it use one opacity value for all your websites, however in the Turn Off the Lights Options page you can enable the opacity slider. So each time you dims the web page, you can see a slider to customize the opacity live. But a way to change the opacity on that kind of page is a good feedback.
About the zoom in/out, you can enable in the Turn Off the Lights Options page -> Advanced Options -> Mouse feature. The function to click through the dark layer, so you can click on all the buttons below this layer.

All welcome feedback and questions is welcome on this official support page: https://www.turnoffthelights.com/support

Have a nice day there.
Thanks,