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| Concern | What to inspect | Typical failure |
|---|---|---|
| Core behavior | Building a Consistent Component Style System | A style system becomes brittle when every component invents its own spacing and state vocabulary. Consistency is mostly a naming and ownership problem before it is a CSS syntax problem. |
| Production test | Real content and constraints | The rule works only for the demo values |
| Maintenance | Scope and override path | A later fix creates another exception |
In production, A style system becomes brittle when every component invents its own spacing and state vocabulary. Consistency is mostly a naming and ownership problem before it is a CSS syntax problem. That is the kind of bug that survives visual spot checks because the stylesheet is syntactically valid while the layout contract is wrong.
<style>.demo { --color-primary:#2563eb; }</style><main class="demo">Example content</main>
The useful mental model here is practical: how tokens, variants, states, and component boundaries form a scalable visual language. When a rule looks obvious but the browser produces something else, start by identifying which constraint or rendering phase is actually winning.
<style>.button[data-variant="danger"] { --button-bg:#b91c1c; }</style><main class="demo"><button type="button">Example action</button></main>
Engineering judgment: Use tokens for repeated decisions and component variants for intentional differences. Avoid one selector that tries to encode every product permutation.
In production, A style system becomes brittle when every component invents its own spacing and state vocabulary. Consistency is mostly a naming and ownership problem before it is a CSS syntax problem. That is the kind of bug that survives visual spot checks because the stylesheet is syntactically valid while the layout contract is wrong.
<style>.button[aria-busy="true"] { cursor:progress; }</style><main class="demo"><button type="button">Example action</button></main>
State is useful here because it demonstrates building a consistent component style system under a concrete input rather than as an abstract property list.
<style>.card__actions { display:flex; gap:.75rem; }</style><main class="card__actions">Example content</main>
Composition is useful here because it demonstrates building a consistent component style system under a concrete input rather than as an abstract property list.
Finish the lesson once you have worked through the material. This awards ★ 30 XP.