:root {
  --bg: #f5f7fb;
  --bg-elevated: #ffffff;
  --bg-card: #ffffff;
  --text: #1a2233;
  --text-dim: #5b6577;
  --border: #e1e6f0;
  --accent: #3d7ee8;
  --accent-text: #ffffff;
  --success: #1a9e5c;
  --danger: #d0374c;
  --radius: 14px;
  --radius-sm: 8px;
  --shadow: 0 1px 2px rgba(20, 30, 60, 0.06), 0 4px 16px rgba(20, 30, 60, 0.05);
  color-scheme: light dark;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #10141d;
    --bg-elevated: #171d29;
    --bg-card: #1a2130;
    --text: #e8ecf5;
    --text-dim: #98a2b8;
    --border: #2a3348;
    --accent: #6ea8ff;
    --accent-text: #0b1220;
    --success: #4ade80;
    --danger: #ff8080;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 4px 20px rgba(0, 0, 0, 0.35);
  }
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  overflow-x: hidden;
}

body {
  font-family: system-ui, -apple-system, "Segoe UI", "Hiragino Kaku Gothic ProN",
    "Hiragino Sans", "Yu Gothic UI", "Noto Sans JP", sans-serif;
  line-height: 1.6;
  -webkit-tap-highlight-color: transparent;
}

.site-header {
  padding: 28px 16px 8px;
  text-align: center;
}
.site-header h1 {
  margin: 0 0 4px;
  font-size: clamp(1.4rem, 4vw, 1.9rem);
  letter-spacing: -0.01em;
}
.site-header .tagline {
  margin: 0;
  color: var(--text-dim);
  font-size: 0.95rem;
}

.mode-tabs {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  gap: 8px;
  max-width: 880px;
  margin: 20px auto 0;
  padding: 8px;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 999px;
  box-shadow: var(--shadow);
}
.tab-btn {
  flex: 1;
  padding: 10px 16px;
  border: none;
  border-radius: 999px;
  background: transparent;
  color: var(--text-dim);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease;
}
.tab-btn:hover { color: var(--text); }
.tab-btn.active {
  background: var(--accent);
  color: var(--accent-text);
}

main {
  max-width: 1080px;
  margin: 0 auto;
  padding: 20px 16px 40px;
}

.panel { display: none; }
.panel.active { display: block; }

.input-area, .output-area, .decode-controls {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  margin-bottom: 18px;
  box-shadow: var(--shadow);
}

label {
  display: block;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-dim);
  margin-bottom: 6px;
}

textarea, select, input[type="text"], input[type="number"] {
  width: 100%;
  font-family: inherit;
  font-size: 0.95rem;
  color: var(--text);
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 12px;
  resize: vertical;
}
textarea:focus, select:focus, input:focus {
  outline: 2px solid var(--accent);
  outline-offset: 1px;
}

#encode-input, #decode-input {
  font-size: 1rem;
}

.results-grid { display: flex; flex-direction: column; gap: 22px; }

.category h2 {
  font-size: 1rem;
  color: var(--text-dim);
  margin: 0 0 10px;
  padding-left: 2px;
  font-weight: 700;
  letter-spacing: 0.02em;
}

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 12px;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 12px;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  gap: 8px;
  min-width: 0;
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.card-header h3 {
  margin: 0;
  font-size: 0.92rem;
  font-weight: 700;
}

.card-note {
  margin: -4px 0 0;
  font-size: 0.75rem;
  color: var(--text-dim);
}
.card-note.error { color: var(--danger); }

.card-params, .params-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.card-params label, .params-row label {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--text-dim);
  margin-bottom: 0;
}
.card-params input, .params-row input {
  width: auto;
  min-width: 0;
  padding: 6px 8px;
  font-size: 0.85rem;
}
.card-params input[type="number"] { width: 4.5em; }
.card-params input[type="text"], .params-row input[type="text"] { width: 9em; }

.card-output {
  width: 100%;
  min-height: 4.4em;
  font-family: ui-monospace, "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.85rem;
  overflow-wrap: anywhere;
  word-break: break-all;
}

.copy-btn {
  align-self: flex-end;
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  color: var(--text);
  font-size: 0.8rem;
  font-weight: 600;
  padding: 6px 14px;
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}
.copy-btn:hover { border-color: var(--accent); color: var(--accent); }
.copy-btn.copied {
  background: var(--success);
  border-color: var(--success);
  color: #fff;
}

.decode-controls select { margin-bottom: 10px; }

.output-area .output-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 6px;
}
.output-area .output-header label { margin-bottom: 0; }

#decode-output {
  font-family: ui-monospace, "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  overflow-wrap: anywhere;
  word-break: break-all;
}

.error-msg {
  margin: 8px 0 0;
  color: var(--danger);
  font-size: 0.85rem;
  min-height: 1.2em;
}

footer {
  max-width: 1080px;
  margin: 0 auto;
  padding: 8px 16px 32px;
  text-align: center;
}
footer p {
  color: var(--text-dim);
  font-size: 0.8rem;
}

@media (max-width: 480px) {
  .mode-tabs { margin: 12px auto 0; border-radius: var(--radius); }
  .tab-btn { font-size: 0.88rem; padding: 10px 8px; }
  main { padding: 14px 10px 32px; }
  .cards { grid-template-columns: 1fr; }
}