Looks great! It took me a few tries to understand how the Settings work and I would explain it in the help if I were you. I was trying to change the theme from dark to light and took me a while to understand that I had to add the new value on the righmost cell instead of changing the default value column :)

In my humble opinion the light theme would be better as a default because I am used to Excel. I suppose most Excel users would say the same.