Website theme should be auto based on user device

[sxflynn]

I appreciate that #47 added an auto theme for the social preview output, however there should also be an auto theme for the website itself. It currently defaults to dark and does not change to light if the user's device is light theme.

[wei]

Thanks for opening the ticket. This was by design but we're open to new PR to add auto theme after #501

[wei]

#501 has been completed. PR welcome for this feature.