:root {
  --page-bg: #f7f8fa;
  --text: #333333;
  --header-bg: #2b3e50;
  --header-text: #ffffff;
  --footer-link: #87ceeb;
  --footer-link-hover: #add8e6;
  --panel-bg: #ffffff;
  --border: #cccccc;
  --drop-bg: #f9f9f9;
  --drop-text: #666666;
  --drop-active: #e8f2ff;
  --file-bg: #2b68b3;
  --file-hover: #235a9c;
  --button-text: #ffffff;
  --clear-bg: #c82333;
  --clear-hover: #b02a37;
  --compare-bg: #1e7e34;
  --compare-hover: #19692c;
  --result-text: #c62828;
  --link: #2b68b3;
  --modal-bg: #fefefe;
  --modal-header: #f5f5f5;
  --modal-heading: #2b3e50;
  --modal-close: #595959;
  --modal-close-hover: #000000;
  --modal-border: #888888;
  --modal-divider: #e0e0e0;
  --shadow: rgba(0, 0, 0, 0.1);
  --modal-shadow: rgba(0, 0, 0, 0.3);
  --overlay: rgba(0, 0, 0, 0.5);
  --header-border: rgba(255, 255, 255, 0.3);
  --header-hover: rgba(255, 255, 255, 0.1);
  --header-border-hover: rgba(255, 255, 255, 0.5);
}

body.dark-mode {
  --page-bg: #1a1a1a;
  --text: #e0e0e0;
  --header-bg: #0d1117;
  --header-text: #e0e0e0;
  --footer-link: #58a6ff;
  --footer-link-hover: #79c0ff;
  --panel-bg: #21262d;
  --border: #30363d;
  --drop-bg: #161b22;
  --drop-text: #b1b1b1;
  --drop-active: #1c2128;
  --file-bg: #79b8ff;
  --file-hover: #a5d0ff;
  --button-text: #0d1117;
  --clear-bg: #ff8a80;
  --clear-hover: #ffb4ad;
  --compare-bg: #7ee787;
  --compare-hover: #a8efae;
  --result-text: #ff8a80;
  --link: #58a6ff;
  --modal-bg: #21262d;
  --modal-header: #161b22;
  --modal-heading: #58a6ff;
  --modal-close: #a9b1ba;
  --modal-close-hover: #e0e0e0;
  --modal-border: #30363d;
  --modal-divider: #30363d;
  --shadow: rgba(0, 0, 0, 0.5);
  --header-border: rgba(255, 255, 255, 0.5);
  --header-hover: rgba(255, 255, 255, 0.2);
  --header-border-hover: rgba(255, 255, 255, 0.7);
}

*, *::before, *::after {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

body {
  font-family: system-ui, sans-serif;
  margin: 0;
  padding: 0;
  background-color: var(--page-bg);
  color: var(--text);
}

header, footer {
  background-color: var(--header-bg);
  color: var(--header-text);
  text-align: center;
  padding: 1rem;
}

footer a {
  color: var(--footer-link);
  text-decoration: none;
  font-weight: bold;
  transition: color 0.3s ease;
}

footer a:hover {
  color: var(--footer-link-hover);
  text-decoration: underline;
}

h1 {
  margin: 0;
  font-size: 2rem;
}

main {
  padding: 2rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.upload {
  display: flex;
  justify-content: space-around;
  flex-wrap: wrap;
  gap: 1rem;
}

.upload-box {
  flex: 1 1 300px;
  min-width: 0;
  background: var(--panel-bg);
  padding: 1rem;
  border-radius: 8px;
  box-shadow: 0 0 10px var(--shadow);
  text-align: center;
}

canvas {
  max-width: 100%;
  margin-top: 1rem;
  border: 1px solid var(--border);
}

.compare-control {
  text-align: center;
}

.result {
  background: var(--panel-bg);
  padding: 1rem;
  border-radius: 8px;
  box-shadow: 0 0 10px var(--shadow);
  text-align: center;
}

#diffRate {
  margin-top: 1rem;
  font-weight: bold;
  color: var(--result-text);
}

/* ドラッグ&ドロップエリア */
.drop-zone {
  border: 2px dashed var(--border);
  border-radius: 8px;
  padding: 2rem 1rem;
  text-align: center;
  background-color: var(--drop-bg);
  transition: all 0.3s ease;
  margin-bottom: 1rem;
}

.drop-zone.dragover {
  border-color: var(--file-bg);
  background-color: var(--drop-active);
  transform: scale(1.02);
}

.drop-zone p {
  margin: 0 0 1rem 0;
  color: var(--drop-text);
  font-size: 0.95rem;
}

/* ファイル入力を隠す */
.drop-zone input[type="file"] {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

/* カスタムファイル選択ボタン */
.file-label {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  padding: 0.5rem 1.5rem;
  background-color: var(--file-bg);
  color: var(--button-text);
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: background-color 0.3s ease;
}

.file-label:hover {
  background-color: var(--file-hover);
}

/* ボタンのスタイル調整 */
button {
  min-width: 44px;
  min-height: 44px;
  padding: 0.5rem 1rem;
  margin: 0.5rem;
  border: none;
  border-radius: 4px;
  background-color: var(--clear-bg);
  color: var(--button-text);
  cursor: pointer;
  font-size: 0.9rem;
  transition: background-color 0.3s ease;
}

button:hover {
  background-color: var(--clear-hover);
}

#compareButton {
  background-color: var(--compare-bg);
  font-size: 1.1rem;
  padding: 0.8rem 2rem;
}

#compareButton:hover {
  background-color: var(--compare-hover);
}

/* ヘッダーの操作ボタンは横並びの1組にまとめる。増えても位置を個別に決めなくてよい。 */
.header-buttons {
  position: absolute;
  right: 1rem;
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

/* 言語切り替えボタン。英語は日本語より長いので幅は文字数に任せる。 */
.lang-toggle {
  background-color: transparent;
  border: 2px solid var(--header-border);
  border-radius: 22px;
  min-width: 44px;
  height: 44px;
  padding: 0 0.9rem;
  margin: 0;
  cursor: pointer;
  font-size: 0.9rem;
  white-space: nowrap;
  transition: all 0.3s ease;
}

.lang-toggle:hover {
  background-color: var(--header-hover);
  border-color: var(--header-border-hover);
}

body.dark-mode .lang-toggle {
  border-color: var(--header-border-hover);
}

/* ダークモード切り替えボタン */
.dark-mode-toggle {
  background-color: transparent;
  border: 2px solid var(--header-border);
  border-radius: 50%;
  width: 44px;
  height: 44px;
  cursor: pointer;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.3s ease;
  padding: 0;
  margin: 0;
}

.dark-mode-toggle:hover {
  background-color: var(--header-hover);
  border-color: var(--header-border-hover);
}

.dark-mode-toggle .dark-icon {
  display: none;
}

header {
  position: relative;
}

/* ダークモード用スタイル */
body.dark-mode {
  background-color: var(--page-bg);
  color: var(--text);
}

body.dark-mode header,
body.dark-mode footer {
  background-color: var(--header-bg);
}

body.dark-mode .upload-box,
body.dark-mode .result {
  background-color: var(--panel-bg);
  box-shadow: 0 0 10px var(--overlay);
}

body.dark-mode .drop-zone {
  background-color: var(--drop-bg);
  border-color: var(--border);
}

body.dark-mode .drop-zone.dragover {
  background-color: var(--drop-active);
  border-color: var(--link);
}

body.dark-mode .drop-zone p {
  color: var(--drop-text);
}

body.dark-mode canvas {
  border-color: var(--border);
}

body.dark-mode .dark-mode-toggle {
  border-color: var(--header-border-hover);
}

body.dark-mode .dark-mode-toggle:hover {
  background-color: var(--header-hover);
  border-color: var(--header-border-hover);
}

body.dark-mode .dark-mode-toggle .light-icon {
  display: none;
}

body.dark-mode .dark-mode-toggle .dark-icon {
  display: block;
}

body.dark-mode h1,
body.dark-mode h2 {
  color: var(--text);
}

body.dark-mode footer a {
  color: var(--link);
}

body.dark-mode footer a:hover {
  color: var(--footer-link-hover);
}

/* ヘルプボタン */
.help-button {
  background-color: transparent;
  border: 2px solid var(--header-border);
  border-radius: 50%;
  width: 44px;
  height: 44px;
  cursor: pointer;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.3s ease;
  padding: 0;
  margin: 0;
  color: var(--button-text);
}

.help-button:hover {
  background-color: var(--header-hover);
  border-color: var(--header-border-hover);
}

.help-button, .dark-mode-toggle, .lang-toggle {
  color: var(--header-text);
}

body.dark-mode .help-button {
  border-color: var(--header-border-hover);
}

body.dark-mode .help-button:hover {
  background-color: var(--header-hover);
  border-color: var(--header-border-hover);
}

/* モーダル */
.modal {
  position: fixed;
  z-index: 1000;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  background-color: var(--overlay);
  backdrop-filter: blur(3px);
}

.modal-content {
  position: relative;
  background-color: var(--modal-bg);
  margin: 2% auto;
  padding: 0;
  border: 1px solid var(--modal-border);
  border-radius: 8px;
  width: 90%;
  max-width: 600px;
  max-height: 90vh;
  display: flex;
  flex-direction: column;
  box-shadow: 0 4px 20px var(--modal-shadow);
}

.modal-content h2 {
  margin: 0;
  padding: 1rem 4.5rem 1rem 1.5rem;
  border-bottom: 1px solid var(--text);
  background-color: var(--modal-header);
  border-radius: 8px 8px 0 0;
}

.modal-body {
  padding: 1.5rem;
  overflow-y: auto;
  flex: 1;
}

.modal-body h3 {
  color: var(--modal-heading);
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

.modal-body h3:first-child {
  margin-top: 0;
}

.modal-body ul, .modal-body ol {
  margin-left: 1.5rem;
  line-height: 1.8;
}

.modal-body li {
  margin-bottom: 0.5rem;
}

.modal-body a {
  color: var(--link);
  text-decoration: none;
}

.modal-body a:hover {
  text-decoration: underline;
}

.modal-close {
  color: var(--modal-close);
  position: absolute;
  right: 0;
  top: 0;
  margin: 0;
  background: var(--modal-header);
  font-size: 28px;
  font-weight: bold;
  cursor: pointer;
  line-height: 20px;
  padding: 1rem 1.5rem;
}

.modal-close:hover,
.modal-close:focus {
  color: var(--modal-close-hover);
  background: var(--modal-header);
}

/* ダークモードのモーダル */
body.dark-mode .modal-content {
  background-color: var(--panel-bg);
  border-color: var(--border);
  color: var(--text);
}

body.dark-mode .modal-content h2 {
  background-color: var(--drop-bg);
  border-bottom-color: var(--border);
  color: var(--text);
}

body.dark-mode .modal-body h3 {
  color: var(--link);
}

body.dark-mode .modal-body a {
  color: var(--link);
}

body.dark-mode .modal-close {
  color: var(--modal-close);
}

body.dark-mode .modal-close:hover,
body.dark-mode .modal-close:focus {
  color: var(--text);
}

/* 追加操作と結果。空の通知は余白も作らない。 */
.hash, .notice {
  overflow-wrap: anywhere;
}

#diffRate, #hashResult {
  white-space: pre-line;
}

#statusMessage:empty, #errorMessage:empty, .notice:empty, .hash:empty,
#matchResult:empty, #hashResult:empty, #diffRate:empty {
  display: none;
}

#errorMessage, .notice {
  color: var(--result-text);
}

#canvas1Copy, #canvas2Copy, #saveDiff {
  background: var(--file-bg);
}

#canvas1Copy:hover, #canvas2Copy:hover, #saveDiff:hover {
  background: var(--file-hover);
}

button:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

button:focus-visible, input:focus-visible + .file-label,
input[type="range"]:focus-visible, a:focus-visible {
  outline: 3px solid var(--link);
  outline-offset: 3px;
}

#tolerance {
  max-width: 100%;
  min-height: 44px;
  vertical-align: middle;
}

/* 英語のボタンは日本語より長い。見出しに重なる前に、ボタンの組を見出しの下へ回す。 */
@media (max-width: 940px) {
  .header-buttons {
    position: static;
    transform: none;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 1rem;
  }
}

@media (max-width: 600px) {
  main {
    padding: 1rem;
  }

  .upload-box {
    flex-basis: 100%;
  }

  .modal-body {
    padding: 1rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    transition: none !important;
  }

  .drop-zone.dragover {
    transform: none;
  }
}