I'm curious about this too. In the past I've used the free themes from Bootswatch: https://bootswatch.com/ https://bootswatch.com/ e.g. Flatly and Darkly can b

I'm curious about this too. In the past I've used the free themes from Bootswatch: https://bootswatch.com/ https://bootswatch.com/ e.g. Flatly and Darkly can be swapped in and used as a light/dark theme easily. Also, means your site doesn't look as generic as the base Bootstrap theme.