First of all, you aren't overthinking. If anyone blames you of that, besides yourself, they're underthinking.
There isn't a day that goes by that I'm not picking at my own code. I'm a 20+ year pro, and I still take introductory HTML5 courses - and guess what - I still learn at least one thing I either forgot, didn't feel the need to remember, or never knew in an ever-changing industry.
CSS Grid is a wonderful example of what I chose to embrace immediately after learning it, but am very hesitant to use it on certain projects. Flexbox was never added to my list of something I'd end up using for any project, but at least I know how to use it correctly.
One of the best sites to browse through, would be Codepen.io. Not everything there is perfect, or even completed, but there are some pens that you will want to fork and sandbox yourself. Check it out when you have a chance.
Here's my collection of pens, which i'll poke around with often, without worrying about getting it perfect. It's a sandbox, so have fun experimenting like I have.