2nd/10_Wiki/Dev/Topic_CSS/CSS_Margin_Collapse.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
css-margin-collapse	CSS Margin Collapse	Frontend	draft	conceptual		margin collapse collapsing margins CSS margin collapsing vertical margin collapse largest margin wins		B	0.89	2026-06-23	2026-06-23			css web frontend w3schools margin box-model	https://www.w3schools.com/css/css_margin_collapse.asp

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).