QR Code React Sass

The project I'm working on is an interesting challenge, but I feel like there are some things I want to learn more about and some aspects that still confuse me. The main obstacle I encountered while building this project was still learning how to use CSS properly, especially in the context of front end development. I find it sometimes difficult to achieve the look I want and apply CSS efficiently. I feel I need to learn more. Do you have any suggestions or resources that can help me understand good CSS usage?