When I signed up on Codecademy, they recommended I complete the “Full Stack Developer” learning path. First up is HTML and CSS. I started the course a couple of weeks ago, and have finished the lessons and quizzes. I’m currently working on what they call “free-form projects” where I’m given code to edit with the end goal of replicating a given webpage. So much of what I’ve done working on these projects is based in Bootstrap, so I’ve put some helpful links on the Resources page (for future reference).
That said, I am a little frustrated with my own timing– the HTML/CSS course is being discontinued this summer and replaced with an HTML5/CSS3 course, which means I will have to re-do everything later. Also, Bootstrap 4 is on the way. At least I will be well-versed in web development!