Write stable declarations, then trace why a value wins. Each lesson makes one concrete CSS decision and names its verification cost.
Lessons
- CSS files and rules: keep presentation out of the document structure
- CSS cascade layers: set precedence before selectors grow
- CSS custom properties: share tokens without losing fallbacks
- CSS inheritance and defaults: reset only the property you mean
- CSS units and functions: size against the right reference
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Common Mistakes
- Do not carry a sample rule into production without checking its containing markup.
- Do not skip keyboard, zoom, or long-content checks when a visual result looks correct.