2nd/10_Wiki/Topic_CSS/CSS_Dropdowns.md

---
id: css-dropdowns
title: "CSS Dropdowns"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["dropdown", "CSS dropdown menu", "hover dropdown", "dropdown box", "pure CSS dropdown"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.89
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "dropdown", "hover", "menu"]
raw_sources: ["https://www.w3schools.com/css/css_dropdowns.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Dropdowns]]

## 🎯 한 줄 통찰 (One-line insight)
A CSS dropdown reveals hidden content on hover by combining a `position: relative` wrapper, an absolutely positioned `display: none` content box, and a `:hover` rule that flips it to `display: block` — no JavaScript required. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Dropdown** — a UI element that displays content (text, links, images) when the user moves over or interacts with a trigger element such as a `div`, `button`, `p`, or `a`. [S1]
- **Wrapper positioning** — the outer `.dropdown` container is given `position: relative` so the dropdown content can be positioned relative to it. [S1]
- **Hidden-by-default content** — `.dropdown-content` starts at `display: none` and `position: absolute`, so it does not occupy space until shown. [S1]
- **Hover reveal** — the `.dropdown:hover .dropdown-content` rule sets `display: block`, exposing the content while the pointer is over the wrapper. [S1]
- **Visual depth** — a `box-shadow` is used to give the dropdown box a floating, layered appearance. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Relative-parent / absolute-child** — pair a `position: relative` wrapper with a `position: absolute` content box so the box anchors to the wrapper. [S1]
- **Hover toggle** — switch a child from `display: none` to `display: block` via a parent `:hover` descendant selector, achieving show/hide without scripting. [S1]
- **Styled trigger button** — a `.dropbtn` class styles the trigger (background color, padding, no border, pointer cursor) and changes color on parent hover. [S1]

## 📖 세부 내용 (Details)
**What is a CSS dropdown?**
A CSS dropdown is a UI element that displays content when users click or hover over a trigger element like a button or link. The trigger can be a `div`, `button`, `p`, or `a` tag, and the hidden dropdown content displays on interaction. [S1]

**Example 1 — Dropdown Box with Text**
A basic hoverable dropdown. The parent uses `position: relative`; the `.dropdown-content` is hidden (`display: none`) and absolutely positioned, with a `min-width` of `130px` and a `box-shadow` for depth. The `:hover` selector reveals it: [S1]
```html
<style>
.dropdown {
  position: relative;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 130px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  padding: 12px 16px;
}

.dropdown:hover .dropdown-content {
  display: block;
}
</style>

<div class="dropdown">Mouse over me!
  <div class="dropdown-content">Hello World!</div>
</div>
```

**Example 2 — Dropdown Menu**
Extends the dropdown into an interactive menu. A styled `.dropbtn` button (green `#4CAF50` background, white text, `16px` padding) triggers the menu; links inside `.dropdown-content` are block-level with padding and no underline, and change background on hover. The button darkens (`#3e8e41`) when the dropdown is hovered: [S1]
```html
<style>
.dropdown {
  position: relative;
}

/* Style the dropdown button */
.dropbtn {
  background-color: #4CAF50;
  color: white;
  padding: 16px;
  font-size: 16px;
  border: none;
  cursor: pointer;
}

/* Dropdown content */
.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 200px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
}

/* Links inside dropdown content */
.dropdown-content a {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
}

/* Change color of dropdown links on hover */
.dropdown-content a:hover {
  background-color: #f1f1f1
}

/* Show the dropdown content on hover */
.dropdown:hover .dropdown-content {
  display: block;
}

/* Change background color of dropdown button on hover */
.dropdown:hover .dropbtn {
  background-color: #3e8e41;
}
</style>

<div class="dropdown">
  <button class="dropbtn">Dropdown Menu</button>
  <div class="dropdown-content">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
</div>
```

## 🛠️ 적용 사례 (Applied in summary)
The two examples on the page are the applied demonstrations: a text dropdown box and a link-based dropdown menu, both shown as complete self-contained markup. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Core relative-parent / hover-reveal pattern (language: CSS):
```css
.dropdown {
  position: relative;
}

.dropdown-content {
  display: none;
  position: absolute;
}

.dropdown:hover .dropdown-content {
  display: block;
}
```

## ⚖️ 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 Advanced Dropdowns]], [[CSS Position]], [[CSS Navigation Bar]]
- **참조 맥락:** Referenced whenever building hoverable menus, tooltips, or pop-over content panels in pure CSS.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Dropdowns — https://www.w3schools.com/css/css_dropdowns.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Dropdowns" page (Astra wiki-curation, P-Reinforce v3.1 format).