You've covered syntax, selectors, colors, the box model, typography, layout (float, position, flexbox, grid), responsive design, transitions and custom properties — everything you need to build real interfaces. This last chapter is an open sandbox: edit the HTML and CSS below and watch the preview update as you type.
A few things to try: switch .card's layout to display: flex and add
gap; give the button a :hover transition; add a second card and lay
both out with display: grid; grid-template-columns: 1fr 1fr;. There's
no wrong answer here — this box is exactly what "Try It Yourself" means
on every chapter in this course.