There is still some work to do on the Dark color scheme, but I do now have it working for when you have set a preference for dark mode in your browser but not on the site. You may use the option in the Tools menu to change your preference to Light if you want to keep your browser preference for dark mode without using the Dark color scheme for this site. To save your preference, you will have to click the Save button, which will run a PHP script to set a cookie with your preference stored in it. You may also have to refresh your cache before pages display properly.
I had wanted to represent each color scheme only once in the CSS, but I got it to work by representing the Light scheme once and the Dark scheme twice. The Light scheme is the default, and it will be overwritten with the Dark scheme under either of two conditions. One is when you have set a preference for a dark scheme in your browser, and you have not overridden this preference by selecting the Light scheme for this site. The other is when you have specified a preference for this site's Dark scheme. Since preferences on the site override preferences set in the browser, this condition is kept less complicated. The System color scheme is now the default, and this tells it to use the browser preferences. If you specifically set the color scheme to Light or Dark, it will use that scheme no matter what your browser preferences are.
There is still some work to do on the Dark color scheme, but I do now have it working for when you have set a preference for dark mode in your browser but not on the site. You may use the option in the Tools menu to change your preference to Light if you want to keep your browser preference for dark mode without using the Dark color scheme for this site. To save your preference, you will have to click the Save button, which will run a PHP script to set a cookie with your preference stored in it. You may also have to refresh your cache before pages display properly.
I had wanted to represent each color scheme only once in the CSS, but I got it to work by representing the Light scheme once and the Dark scheme twice. The Light scheme is the default, and it will be overwritten with the Dark scheme under either of two conditions. One is when you have set a preference for a dark scheme in your browser, and you have not overridden this preference by selecting the Light scheme for this site. The other is when you have specified a preference for this site's Dark scheme. Since preferences on the site override preferences set in the browser, this condition is kept less complicated. The System color scheme is now the default, and this tells it to use the browser preferences. If you specifically set the color scheme to Light or Dark, it will use that scheme no matter what your browser preferences are.