Hi, folks I hope this helps you.
So, I was trying to upload an Elementor theme from Evanto to show my friend how to install a theme. However, I got an error message saying:
"The package could not be installed. The theme is missing the style CSS stylesheet Theme installation."
I was confused at first, but then I realized that the "theme" was not a Theme! It was a zipped template with a set of JSON files that needed to be imported into Elementor.
After unzipping the file, I found a folder called "Template' with several JSON files that I needed to import into Elementor.
To fix the issue: I zipped up the "Template" folder and uploaded the "Template.zip" file into Elementor.
This successfully installed all the pages.
Side note I had Elementor's HELLO theme installed, and I was using Elementor Pro.
Hope this helps...
PS: That's not my real voice. I was playing. :)