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<style>.card > h2 { margin-block-start:0; }</style><main class="demo"><article class="card"><h2>Example heading</h2></article></main>
Engineering judgment: Structural selectors are most maintainable when the DOM relationship is stable and meaningful, not when they are used to avoid naming a real component state.
| Concern | What to inspect | Typical failure |
|---|---|---|
| Core behavior | Combinators and Structural Selectors | Descendant selectors can silently reach deep into unrelated markup. Prefer direct relationships when the component contract is meant to be explicit. |
| 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, Descendant selectors can silently reach deep into unrelated markup. Prefer direct relationships when the component contract is meant to be explicit. That is the kind of bug that survives visual spot checks because the stylesheet is syntactically valid while the layout contract is wrong.
The useful mental model here is practical: how child, descendant, sibling, and structural pseudo-class relationships express layout and semantics. When a rule looks obvious but the browser produces something else, start by identifying which constraint or rendering phase is actually winning.
<style>label + .hint { margin-block-start:.25rem; }</style><main class="demo"><div class="hint"><span>Label</span><span>Related item</span></div></main>
A good CSS change narrows the problem. Structural selectors are most maintainable when the DOM relationship is stable and meaningful, not when they are used to avoid naming a real component state. This keeps the rule understandable when content, theme, or viewport conditions change later.
<style>.tab[aria-selected="true"] ~ .panel { display:block; }</style><main class="demo"><div class="tab"><span>Label</span><span>Related item</span></div></main>
General sibling is useful here because it demonstrates combinators and structural selectors under a concrete input rather than as an abstract property list.
<style>.demo { li:nth-child(even) { background:#f8fafc; }; }</style><main class="demo">Example content</main>
Structural row is useful here because it demonstrates combinators and structural selectors 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.