Wanted to Build a website builder like durable, but I hit a wall...

Hi, this is my birth my first multi Tennant project, I want to make a easy website builder that makes simple but pretty websites easily and maybe integrate AI to help help with them for clients who can create accounts and start building visually right away,

I made big progress and everything is working fine all the elements and everything,

But the problem here is that the website that my platform generates and make are very basic and very unattractive, I tried to make them better looking like the durable ones, but I had no luck if anyone can help me structure my builder so that it makes my nice ui designs that would be great