2nd/10_Wiki/Topic_CSS/CSS_Z_Index.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-z-index	CSS Z-index	Frontend	draft	conceptual		z-index stack order stacking order CSS z index layer order stacking context		B	0.88	2026-06-23	2026-06-23			css web frontend w3schools position z-index	https://www.w3schools.com/css/css_z-index.asp

CSS Z-index

🎯 한 줄 통찰 (One-line insight)

The z-index property sets the stack order of positioned elements — higher values render in front of lower ones — and it only works on positioned elements and flex items. [S1]

🧠 핵심 개념 (Core concepts)

• stack order — z-index specifies the stack order of positioned elements, determining which elements appear in front of or behind others. [S1]
• positive or negative — elements can have positive or negative z-index values. [S1]
• higher wins — higher z-index values always appear above lower ones. [S1]
• only on positioned elements — z-index only works on positioned elements (position: absolute, position: relative, position: fixed, or position: sticky) and flex items. [S1]
• default order — without a z-index, elements render in HTML source order. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Send behind with negative z-index — give an absolutely positioned element z-index: -1 to render it behind text/content. [S1]
• Explicit layering — assign ascending z-index values to sibling boxes to control which overlaps which, independent of source order. [S1]

📖 세부 내용 (Details)

CSS The z-index Property [S1] z-index specifies the stack order of positioned elements, determining which elements appear in front or behind others. Elements can have positive or negative z-index values.

Note: z-index only works on positioned elements (position: absolute, position: relative, position: fixed, or position: sticky) and flex items. [S1]

First example — negative z-index puts an image behind text [S1] The CSS rule uses position: absolute, left: 0px, top: 0px, and z-index: -1. The HTML includes a heading "This is a heading". The image with z-index of -1 renders behind the text. The page did not provide the full verbatim CSS rule block — Not found in source.

Second example — higher z-index appears above lower [S1] CSS classes defined:

• .container with position: relative
• .black-box with z-index: 1, plus border and margins
• .gray-box with z-index: 3, light gray background
• .green-box with z-index: 2, light green background

HTML structure: a container div holding three nested divs representing the three boxes. The gray box (z-index 3) sits on top, then green (2), then black (1). The full verbatim CSS/HTML block was not provided in the fetched source — Not found in source.

Third example — rendering order without z-index [S1] Code identical to the second example but omitting all z-index declarations, showing that elements render in HTML source order.

Property reference [S1]

Property	Description
z-index	Sets the stack order of an element

🛠️ 적용 사례 (Applied in summary)

The page's applied examples are: an image sent behind a heading via z-index: -1; three overlapping boxes layered by ascending z-index (gray 3 on top, green 2, black 1); and the same three boxes without z-index to show default source-order stacking. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Send a positioned element behind content (language: CSS):

img {
  position: absolute;
  left: 0px;
  top: 0px;
  z-index: -1;
}

Layer sibling boxes by explicit stack order (language: CSS):

.container {
  position: relative;
}
.black-box {
  z-index: 1;
}
.green-box {
  z-index: 2;
}
.gray-box {
  z-index: 3;
}

Note: the page described these declarations but did not present the complete rule blocks verbatim; the snippets above reflect the described properties — additional rule details Not found in source. [S1]

⚖️ 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: 0.88
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: CSS Tutorial
• 관련 개념: CSS Position Fixed and Absolute, CSS Position Sticky, CSS Position Offsets
• 참조 맥락: Referenced whenever positioned elements overlap and their front-to-back order must be controlled.

📚 출처 (Sources)

• [S1] W3Schools — CSS Z-index — https://www.w3schools.com/css/css_z-index.asp

📝 변경 이력 (Change history)

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