Not related to BSS, but about learning bootstrap. I just noticed that an excellent course (I followed it 2 years ago) is again available, for free at EDX.
Module 1: Getting Started with Bootstrap
During our first module we'll cover the basics of Bootstrap and the grid system. You'll see how to obtain and add Bootstrap to your pages, and why Bootstrap makes developing responsive pages simpler than using CSS directly. We'll also explain how the grid system works to layout your pages.
Module 2: Page Design and Data Display
Bootstrap offers several features to ensure your page is designed optimally for all screen sizes. You'll examine how to best use those capabilities to ensure users can easily consume the data they need regardless of their device type. You'll also see how to use some of the advanced components, or controls, that Bootstrap offers.
Module 3: Forms and user interaction
We'll close our exploration of Bootstrap by taking a look at how we can obtain data from the user and provide feedback. Bootstrap offers great support for customizing forms, and several options to let the user know when the form is correct or incorrect. You'll see how to add alerts and modal dialog boxes, as well as inline validation and data prompts.