HTML says what content is; CSS (Cascading Style Sheets) says how it looks. Every Bootstrap 2,007 class in Bootstrap is CSS underneath. You state which elements get which values, and the browser computes the result for every element on every frame.
CSS has changed more since 2020 than in the decade before. Nesting, cascade layers, container queries, :has(), subgrid and anchor positioning now work in all three major engines, and many jobs that once needed JavaScript or a preprocessor take a few lines of plain CSS.
This chapter teaches that modern language, from syntax and the cascade to animation and responsive design, and ends with the tools around it.
What you will learn:
How the cascade, inheritance and specificity decide every value
Units, colors, custom properties, selectors and at-rules
The box model, flexbox, grid and anchor positioning
Smooth transitions and animations, and responsive design with media and container queries
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