In the php.ini did you set both the max post size and the max upload size? Both need to be large enough to support your theme.

Second you said you game all the root read write permissions. Are these files owned by root or your www-data user? I would recommend ensuring the ownership of these files by running:

chown -Rf www-data:www-data /var/www

I solved it. We have to change
post_max_size in php.ini. I did everything I could, didn’t work, even killed my droplet and started again… but when I changed it, it worked!

; Maximum allowed size for uploaded files.
upload_max_filesize = 40M

**; Must be greater than or equal to upload_max_filesize
post_max_size = 40M**