Throughout the book, I've used Chrome as my browser because of its DevTools, among other things, but other browsers have similar tools. We'll use DevTools to explore code directly in the browser.
I've also used macOS throughout. If you're a Windows user and I refer to the command (cmd) key anywhere in the book, you should pretend that I am referring to the Ctrl key. Other than that, I don't think this will be an issue.
I have used the text editor Sublime Text 3. I should say that Sublime isn't the only good one out there. There are others like Atom and Visual Studio Code that do many of the same things.
Even though this book is on mastering CSS, we can't do much with CSS without HTML. So, we'll be working in HTML quite a bit. The goal is to use very clean, semantic HTML; that's what we want to aim for.