Yep, agree. Starting with Bootstrap is fairly frictionless, it has good library support, and there are heaps of documentations/examples/tutorials easily available. And if you need to change the look and feel, you can swap out the bootstrap.css file with one of the examples from Bootswatch - https://bootswatch.com/
Bootswatch is awesome! Recently I’ve just been getting the original Sass files and customizing there, and setting up a gulp pipeline to build my modified bootstrap CSS file. Works great for most things.
As an alternative to Bootstrap, there is also Bulma https://bulma.io/
Bulma's what I used for a recent project of mine¹, and while it did take some tinkering² to get it looking decent with minimal HTML pollution, I've been happy enough with it that I'll probably keep using it for new projects (and possibly redo some existing websites with it).