Add custom theme support

[unitythemaker]

Hey, I'm a fan of catppuccin theme and want to see it in my new tab too. I set my everything to catppuccin theme and it would be awesome if I was able to set it too. I want you to add a feature to place my CSS and use it as my theme.

[idoshamun]

Hi @unitythemaker,

Thanks for the suggestion! 🙏

[donbignose]

I was about to create the same feature request, some theme customization would be awesome as most people using daily.dev put it on the browser homepage.