My CSS is a mess. I always start off with good intentions but once things ramp up my system falls apart.

I've primarily tried using BEM in the past but have had difficulty sticking to this formula. It's too rigid. I'm looking for something simpler. Something that sets me up to create reusable widgets but also incorporates custom styling in a way that is easy to read and find what I'm looking for. I want equal parts structure and flexibility. But I know that's a tall and basically impossible order.

Do you have a CSS system you love? How do you keep your styling organized in a way that you can look at your html and know exactly where to go to make changes?

*edit: I write my CSS in SCSS. I'm looking for help in organizing the SCSS files and classes.