I'm exactly the same. What helped me was Tailwind + commercial TailwindUI library, which was more than worth the money. I just used the pre-built components for both the application and marketing site, and over time started to iterate on my own. I still wouldn't be able to build something that looks good from scratch, but I find evolving an existing good design to be much easier. Got many compliments on my app's UI, which is funny considering how non-intuitive I find design to be.