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Antigravity Agent e9cbf23ab5 docs(10_Wiki): Dev 폴더 누락분 반영 — Topic_Programming으로 통합

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2026-07-05 00:39:13 +09:00

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title

CSS Margin Collapse

🎯 한 줄 통찰 (One-line insight)

Top and bottom margins of elements are sometimes collapsed into a single margin that is equal to the largest of the two margins — this only happens with top and bottom margins, never left and right. [S1]

🧠 핵심 개념 (Core concepts)

Definition — top and bottom margins of elements are sometimes collapsed into a single margin that is equal to the largest of the two margins. [S1]
Largest wins — the resulting single margin equals the larger of the two adjacent margins, not their sum. [S1]
Vertical only — this does not happen on left and right margins, only top and bottom margins. [S1]

🧩 추출된 패턴 (Extracted patterns)

max, not sum — when two vertical margins meet, the gap is max(margin_a, margin_b), not margin_a + margin_b. [S1]
Horizontal exemption — never rely on collapse for left/right spacing; it applies only to top/bottom. [S1]

📖 세부 내용 (Details)

CSS Margin Collapse [S1] Top and bottom margins of elements are sometimes collapsed into a single margin that is equal to the largest of the two margins.

This does not happen on left and right margins! Only top and bottom margins! [S1]

Example — an h1 with a bottom margin and an h2 with a top margin: [S1]

h1 {
  margin: 0 0 50px 0;
}

h2 {
  margin: 20px 0 0 0;
}

The h1 element has a bottom margin of 50px and the h2 element has a top margin set to 20px. Common sense would seem to suggest that the vertical margin between the h1 and the h2 would be a total of 70px (50px + 20px). But due to margin collapse, the actual margin ends up being 50px. [S1]

🛠️ 적용 사례 (Applied in summary)

The page's own applied example is the h1/h2 stylesheet above, which demonstrates that adjacent 50px and 20px vertical margins collapse to a single 50px gap rather than summing to 70px. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Adjacent vertical margins that collapse to the larger value (language: CSS):

h1 {
  margin: 0 0 50px 0;
}

h2 {
  margin: 20px 0 0 0;
}

⚖️ 모순 및 업데이트 (Contradictions & updates)

No contradictions found in the source.

✅ 검증 상태 및 신뢰도

상태: draft
검증 단계: conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
신뢰 점수: 0.89
중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

상위/루트: CSS Tutorial
관련 개념: CSS Margins, CSS Border Sides, CSS Border Shorthand
참조 맥락: A box-model gotcha to keep in mind whenever vertical spacing between stacked elements matters.

📚 출처 (Sources)

[S1] W3Schools — CSS Margin Collapse — https://www.w3schools.com/css/css_margin_collapse.asp

📝 변경 이력 (Change history)

2026-06-23: Initial draft synthesized from the W3Schools "CSS Margin Collapse" page (Astra wiki-curation, P-Reinforce v3.1 format).

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