Dark Mode for the forum

[AnimalToyForum]

As per the DinoToyForum, we now have a dark mode!

I've finally developed a 'dark mode' for the forum! This is something I've wanted to implement for a long time and people have requested it over the years, but I needed to work out how. I had some time off work this week, and the recent funds I received from supporters helped spur me into action. So, anyone who enjoys the dark mode can thank them as well as me!

The default theme for guests is still light, but members can switch between the light and dark mode using the toggle button in the top menu.

Personally, I'm not keen on dark modes myself, so I won't be using it, but hopefully it benefits some members. I can still make further adjustments to the colours so please let me know if you have any feedback or suggestions to improve it. One minor issue we've identified is the colour of usernames and some titles is sometimes difficult to read. I'm a bit hamstrung by this because those are controlled by the core not the theme. So, if I adjust it in the core to make it look good on one theme, it may look worse on the other. But I'll see if I can find a happy medium if anything is completely illegible.

I might also look at creating a separate top banner for dark mode.

Thanks to all the supporters for helping make this happen!