If you are good at ES6 and css, then you’re halfway there. You can build a full stack web application if you know JS with the help of some frameworks. My personal preference for a JS frontend framework is React and for the backend, I prefer express which runs atop node. It is definitely easier in 2020 to develop a web application but the JS ecosystem is too fragmented these days so avoid the shiny object syndrome if you’re serious about making something. npm is a module registry and you can pull in 3rd party dependencies for your app from there, so yeah you might have to learn to navigate your way around it. jenkins and docker are not so necessary in the initial phases as you can offload CI and Cd to SaaS providers such as netlify but the pricing of these providers is steep so you might want to move on from them.