Yes! You can edit the date, time, font, theme color, and clock size directly inside the Page. It's fully flexible and easy to tweak. Just press the Settings icon in the top right corner of the page.
You can just type the name of your desired font (e.g: Roboto / Open Sans / Lobster / Smooch / Nova Mono) in the font family box. The website will automatically apply the font in real-time. You can view your desired font at Fontsource or Google Fonts
You can easily fix it by changing the text color from black to white (or any color other than black) before enabling dark mode. You can do this from the settings menu in the top-right corner.