I don't even find it that hard to customize. I'm a backend dev at heart, but I develop my own niche side projects. I would use something like Symfony's Webpack

I don't even find it that hard to customize. I'm a backend dev at heart, but I develop my own niche side projects. I would use something like Symfony's Webpack Encore (but if I had to start over, I might use something lightweight like Parcel.js, I might migrate though), then let a "yarn watch" run in the background and it would re-compile in 2-3 seconds. While I'm building my product and doing marketing and making sure it is performant and up all the time, I don't have too much time to adjust the details of the menu dropdown in mobile view (or even figure out how to do it). Bootstrap also has utilities now (e.g. "py-md-3" for a large padding in the y axis - top and bottom - in larger screens) and that's good enough for me as a solo-dev for my own side project. Adjusting the border radius and the shadow in the "btn" class in the Sass already gives it a different feel.