Bootstrap

In my workplace we use bootstrap for every project, it's easy to use and with little effort you can make websites that are mobile friendly, but...

Bootstrap is limited in it's structure, yes it's great for quick layout and responsiveness but if you want to change some col size or create a new @media break point you need to lean basic css, you want to change or add to bootstrap you need to learn css to understand what is happening in order to change or add what you need.

We have alot of client requests that bootstrap is not built for, so we created our own css that adds onto the core of bootstrap, we always add to it and sometimes the operation that some classes in bootstrap does is not what we want, so we change them.

For me it's very important to learn the basics if you want to understand and change how bootstrap work and in general its good to have solid basics if you plan to create live websites.