When developing large scale applications, it can be a great idea to use a framework. I am an experienced React developer, building small to large scale applications. I also have used many other frameworks such as Meteor, Vue JS, and Angular JS. I think frameworks are great, but they're not always a good choice. When sizing up a project, make sure to do due diligence when selecting a framework, you may find you don't even need one!
Applications are fun to build, but making them beautiful is just as important. I ❤️ building beautiful things and I primarily use CSS to accomplish that. When starting a project I also look at what I am trying to accomplish with styles and find tools to fit that goal. I have used CSS, CSS Modules, SCSS (Sass), CSSinJS, and many style frameworks as well. I try to followBEM conventions when working with non scoped CSS.