---
id: css-image-modal
title: "CSS Image Modal"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["modal image", "image lightbox", "popup image", "responsive modal", "image gallery modal"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "images", "modal"]
raw_sources: ["https://www.w3schools.com/css/css3_images_modal.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Image Modal]]

## 🎯 한 줄 통찰 (One-line insight)
A modal image (lightbox) lets users click a gallery thumbnail to open a larger version in a full-screen overlay, built from a hidden fixed-position modal that JavaScript shows and hides. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Modal overlay** — the modal is a full-viewport layer (`position: fixed`, `width: 100%`, `height: 100%`) hidden by default with `display: none` and shown via JavaScript. [S1]
- **Dim backdrop** — a semi-transparent background `rgba(0, 0, 0, 0.8)` and high `z-index: 1000` darken the page behind the enlarged image. [S1]
- **Zoom-in animation** — a `@keyframes zoomIn` animation scales the modal content from `0.6` to `1` when it opens. [S1]
- **Close control** — a `.close` "×" (`&times;`) element in the top-right corner closes the modal. [S1]
- **Caption** — a `.caption` element shows the image's label, populated from the trigger's `onclick` argument. [S1]
- **JavaScript control** — `openModal()` sets `display: "flex"` and adds a `show` class; `closeModal()` removes the class and hides the modal after a 300ms delay. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Hidden fixed layer toggled by JS** — keep the modal `display: none`, then switch to a flex layout on demand to center the enlarged content. [S1]
- **Class-driven transition + timed teardown** — add a `show` class to animate in, and on close remove it and use `setTimeout` so the exit transition finishes before `display: none`. [S1]
- **Data passed via onclick args** — the gallery image's `onclick` passes the modal id and caption text directly into the handler. [S1]

## 📖 세부 내용 (Details)
The W3Schools example builds a responsive modal image gallery in a single HTML document combining CSS and JavaScript. [S1]

```html
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

h1 {
  text-align: center;
  padding: 20px;
}

.gallery {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-start;
  padding: 0 15px;
}

.gallery-item {
  position: relative;
  width: calc(25% - 20px);
  height: auto;
  margin: 10px;
  cursor: pointer;
  transition: transform 0.5s ease;
}

.gallery-item:hover {
  transform: scale(1.1);
}

/* The Modal (background) */
.modal {
  display: none;
  position: fixed;
  z-index: 1000;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.8);
  align-items: center;
  justify-content: center;
  transition: opacity 0.5s ease;
}

/* Modal content (image) */
.modal-content {
  position: relative;
  width: 90%;
  height: auto;
  max-width: 90%;
  max-height: 90%;
  border-radius: 5px;
  overflow: hidden;
  animation: zoomIn 0.5s;
}

@keyframes zoomIn {
  from {transform: scale(0.6);}
  to {transform: scale(1);}
}

.modal.show {
  display: flex;
  opacity: 1;
}

/* Close button */
.close {
  position: absolute;
  top: 10px;
  right: 15px;
  color: #ffffff;
  font-size: 35px;
  font-weight: bold;
  cursor: pointer;
  transition: transform 0.3s;
}

/* Caption of modal image */
.caption {
  position: absolute;
  bottom: 15px;
  width: 100%;
  text-align: center;
  color: #ffffff;
  font-size: 24px;
}

@media screen and (max-width: 768px) {
  .gallery-item {
    width: calc(50% - 20px);
  }
}

@media screen and (max-width: 480px) {
  .gallery-item {
    width: calc(100% - 20px);
  }
}
</style>
</head>
<body>

<h1>Responsive Modal Images</h1>

<div class="gallery">
  <img src="img_5terre.jpg" alt="Cinque Terre" class="gallery-item" onclick="openModal('modal1', 'Cinque Terre')">
  <img src="img_forest.jpg" alt="Forest" class="gallery-item" onclick="openModal('modal2', 'Forest')">
  <img src="img_lights.jpg" alt="Northern Lights" class="gallery-item" onclick="openModal('modal3', 'Nothern Lights')">
  <img src="img_mountains.jpg" alt="Mountains" class="gallery-item" onclick="openModal('modal4', 'Mountains')">
</div>

<div id="modal1" class="modal">
  <span class="close" onclick="closeModal('modal1')">&times;</span>
  <img src="img_5terre.jpg" alt="Cinque Terre" class="modal-content">
  <div class="caption"></div>
</div>

<div id="modal2" class="modal">
  <span class="close" onclick="closeModal('modal2')">&times;</span>
  <img src="img_forest.jpg" alt="Forest" class="modal-content">
  <div class="caption"></div>
</div>

<div id="modal3" class="modal">
  <span class="close" onclick="closeModal('modal3')">&times;</span>
  <img src="img_lights.jpg" alt="Northern Lights" class="modal-content">
  <div class="caption"></div>
</div>

<div id="modal4" class="modal">
  <span class="close" onclick="closeModal('modal4')">&times;</span>
  <img src="img_mountains.jpg" alt="Mountains" class="modal-content">
  <div class="caption"></div>
</div>

<script>
function openModal(modalId, caption) {
  let modal = document.getElementById(modalId);
  modal.style.display = "flex";
  modal.classList.add("show");
  let message = modal.querySelector(".caption");
  message.innerText = caption;
}

function closeModal(modalId) {
  let modal = document.getElementById(modalId);
  modal.classList.remove("show");
  setTimeout(function () {
    modal.style.display = "none";
    modal.querySelector(".caption").innerText = "";
  }, 300);
}
</script>

</body>
</html>
```

**Key components**
- **Modal container** — `display: none` initially, `position: fixed`, `z-index: 1000`, dark semi-transparent background `rgba(0, 0, 0, 0.8)`. [S1]
- **Animation** — zoom effect defined with `@keyframes zoomIn` scaling from `0.6` to `1`. [S1]
- **JavaScript** — `openModal()` retrieves the element by id, sets display to `flex`, adds the `show` class, and populates the caption; `closeModal()` removes the `show` class and hides the modal after a 300ms delay. [S1]
- **Responsive design** — media queries adjust gallery items from `25%` width (desktop) to `50%` (tablets, ≤768px) to `100%` (mobile, ≤480px). [S1]

## 🛠️ 적용 사례 (Applied in summary)
The full responsive modal-image gallery above is the source's applied case, integrating a flex gallery, a fixed overlay modal, a zoom animation, a close button, captions, and the open/close JavaScript. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Toggle-by-class modal control (language: JavaScript):
```javascript
function openModal(modalId, caption) {
  let modal = document.getElementById(modalId);
  modal.style.display = "flex";
  modal.classList.add("show");
  modal.querySelector(".caption").innerText = caption;
}

function closeModal(modalId) {
  let modal = document.getElementById(modalId);
  modal.classList.remove("show");
  setTimeout(function () {
    modal.style.display = "none";
    modal.querySelector(".caption").innerText = "";
  }, 300);
}
```

## ⚖️ 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:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Image Hover]], [[CSS Image Styling]], [[CSS Animations]], [[CSS Position]]
- **참조 맥락:** Referenced when building an image lightbox or click-to-enlarge gallery.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Image Modal — https://www.w3schools.com/css/css3_images_modal.asp

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