:root {
  --bg: #f6f8fb;
  --surface: #ffffff;
  --surface-2: #eef2f7;
  --border: #d9e0ea;
  --text: #1b2430;
  --text-muted: #5a6675;
  --accent: #2f6df6;
  --accent-hover: #1e57d6;
  --accent-soft: #e7effe;
  --danger: #d64545;
  --ok: #1f9d55;
  --radius: 12px;
  --shadow: 0 1px 3px rgba(16, 24, 40, 0.08), 0 1px 2px rgba(16, 24, 40, 0.04);
  --mono: ui-monospace, "SFMono-Regular", "Menlo", "Consolas", monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

[data-theme="dark"] {
  --bg: #0f141b;
  --surface: #171e27;
  --surface-2: #1e2732;
  --border: #2a3542;
  --text: #e6ebf2;
  --text-muted: #9aa7b6;
  --accent: #4d86ff;
  --accent-hover: #6b9bff;
  --accent-soft: #1a2740;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.4);
}

* { box-sizing: border-box; }

html, body { margin: 0; padding: 0; }

body {
  font-family: var(--sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

.container {
  width: 100%;
  max-width: 960px;
  margin: 0 auto;
  padding: 0 1.25rem;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.skip-link {
  position: absolute;
  left: -999px;
}
.skip-link:focus {
  left: 1rem;
  top: 1rem;
  background: var(--surface);
  padding: 0.5rem 0.75rem;
  border-radius: 8px;
  z-index: 100;
}

/* Header */
.site-header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 20;
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 60px;
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  color: var(--text);
}
.brand:hover { text-decoration: none; }
.brand-mark { font-size: 1.35rem; }
.site-nav {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}
.site-nav a { color: var(--text-muted); font-weight: 500; }
.site-nav a:hover { color: var(--text); text-decoration: none; }
.theme-toggle {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  width: 34px;
  height: 34px;
  border-radius: 8px;
  cursor: pointer;
  font-size: 1rem;
}
.theme-toggle:hover { border-color: var(--accent); }

/* Hero */
.hero {
  padding: 3rem 0 1.5rem;
  text-align: center;
}
.hero h1 { font-size: 2.4rem; margin: 0 0 0.5rem; }
.tagline { color: var(--text-muted); font-size: 1.1rem; margin: 0; }

/* Tool grid */
.tools-section { padding: 1.5rem 0 3rem; }
.category-title {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin: 2rem 0 0.75rem;
}
.tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}
.tool-card {
  display: flex;
  gap: 0.9rem;
  align-items: flex-start;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.1rem;
  box-shadow: var(--shadow);
  color: var(--text);
  transition: border-color 0.15s, transform 0.15s;
}
.tool-card:hover {
  text-decoration: none;
  border-color: var(--accent);
  transform: translateY(-2px);
}
.tool-icon { font-size: 1.6rem; line-height: 1; }
.tool-body { display: flex; flex-direction: column; gap: 0.25rem; }
.tool-title { font-weight: 600; }
.tool-summary { color: var(--text-muted); font-size: 0.9rem; }
.empty-state { color: var(--text-muted); }

/* Tool page */
.tool-page { padding: 2rem 0 3rem; }
.breadcrumb {
  display: flex;
  gap: 0.5rem;
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-bottom: 1rem;
}
.tool-header h1 {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin: 0 0 0.35rem;
}
.tool-header .tool-summary { margin: 0 0 1.5rem; }

/* Forms */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.5rem;
}
.form-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem 1.25rem;
}
.field { display: flex; flex-direction: column; gap: 0.35rem; }
.field label { font-size: 0.85rem; font-weight: 600; }
.field .hint { font-size: 0.78rem; color: var(--text-muted); }
.field input,
.field select {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  padding: 0.55rem 0.65rem;
  font-size: 0.95rem;
  font-family: var(--mono);
}
.field textarea {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  padding: 0.55rem 0.65rem;
  font-size: 0.9rem;
  font-family: var(--mono);
  resize: vertical;
  line-height: 1.5;
}
.field input:focus,
.field select:focus,
.field textarea:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-soft);
}

.actions { margin-top: 1.25rem; display: flex; gap: 0.75rem; flex-wrap: wrap; }
.btn {
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 0.6rem 1.2rem;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
}
.btn:hover { background: var(--accent-hover); }
.btn.secondary {
  background: var(--surface-2);
  color: var(--text);
  border: 1px solid var(--border);
}

/* Results */
.result-summary {
  margin-top: 1.5rem;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 0.75rem;
}
.stat {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.85rem 1rem;
}
.stat .label {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
}
.stat .value { font-family: var(--mono); font-size: 1.25rem; font-weight: 600; }
.stat .value.small { font-size: 1rem; }

.msg { margin-top: 1rem; padding: 0.75rem 1rem; border-radius: 8px; font-size: 0.9rem; }
.msg.error { background: rgba(214, 69, 69, 0.12); color: var(--danger); }
.msg.ok { background: rgba(31, 157, 85, 0.12); color: var(--ok); }
.msg.hidden { display: none; }

.table-wrap { margin-top: 1.5rem; overflow-x: auto; }
table.results {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--mono);
  font-size: 0.88rem;
}
table.results th,
table.results td {
  text-align: right;
  padding: 0.5rem 0.7rem;
  border-bottom: 1px solid var(--border);
  white-space: nowrap;
}
table.results th {
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
  font-size: 0.72rem;
  letter-spacing: 0.04em;
}
table.results tbody tr:hover { background: var(--surface-2); }
table.results tr.best td { background: var(--accent-soft); }

table.results.ascii td.ch { text-align: center; font-size: 1.05rem; }
table.results.ascii td.name { text-align: left; color: var(--text-muted); }

/* Code output */
.code-block {
  position: relative;
  margin-top: 1.5rem;
}
.code-block pre {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1rem 1rem;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 0.85rem;
  margin: 0;
}
.copy-btn {
  position: absolute;
  top: 0.6rem;
  right: 0.6rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 0.25rem 0.6rem;
  font-size: 0.78rem;
  cursor: pointer;
  color: var(--text);
}

.section-label {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
  margin: 1.75rem 0 0.5rem;
}

.prose { color: var(--text); }
.prose h2 { margin-top: 2rem; }
.prose code {
  font-family: var(--mono);
  background: var(--surface-2);
  padding: 0.1rem 0.35rem;
  border-radius: 5px;
  font-size: 0.9em;
}
.prose .formula {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
  font-family: var(--mono);
  text-align: center;
  overflow-x: auto;
}

/* Bit grid (Bit Manipulator) */
.bit-grid {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 4px;
  margin: 1.5rem 0;
}
.bit-cell {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 30px;
  padding: 0.3rem 0.2rem;
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 6px;
  cursor: pointer;
  font-family: var(--mono);
  color: var(--text-muted);
  transition: background 0.1s, color 0.1s, border-color 0.1s;
}
.bit-cell:hover { border-color: var(--accent); }
.bit-cell.on {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
.bit-cell .bit-val { font-size: 1.05rem; font-weight: 600; line-height: 1.2; }
.bit-cell .bit-idx { font-size: 0.6rem; opacity: 0.7; }
.bit-sep { width: 10px; }

/* Bit field tags (IEEE-754) */
.bits-line {
  overflow-x: auto;
  margin: 0.5rem 0 1.25rem;
}
.bits-line code {
  font-family: var(--mono);
  font-size: 1rem;
  letter-spacing: 1px;
  white-space: nowrap;
}
.tag {
  padding: 0.1rem 0.3rem;
  border-radius: 5px;
  font-family: var(--mono);
}
.tag.sign { background: rgba(214, 69, 69, 0.22); color: var(--danger); }
.tag.exp { background: rgba(47, 109, 246, 0.22); color: var(--accent); }
.tag.man { background: rgba(31, 157, 85, 0.22); color: var(--ok); }

/* Tabs (Text Repair Studio) */
.tabs {
  display: flex;
  gap: 0.25rem;
  border-bottom: 1px solid var(--border);
  margin: -0.25rem 0 1.25rem;
}
.tab {
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  color: var(--text-muted);
  padding: 0.6rem 0.9rem;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  margin-bottom: -1px;
}
.tab:hover { color: var(--text); }
.tab.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}
table.results.candidates td { vertical-align: top; }

/* Split two-pane layout (Diff / Markdown Previewer) */
.split-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}
@media (max-width: 700px) {
  .split-grid { grid-template-columns: 1fr; }
}
.split-grid textarea { min-height: 220px; }

/* Rendered output panel (Markdown preview, diff view) */
.output-panel {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.75rem 0.9rem;
  min-height: 220px;
  overflow: auto;
  font-size: 0.92rem;
}
.output-panel.mono { font-family: var(--mono); white-space: pre-wrap; word-break: break-word; }
.output-panel :first-child { margin-top: 0; }
.output-panel :last-child { margin-bottom: 0; }
.output-panel h1, .output-panel h2, .output-panel h3 { line-height: 1.3; }
.output-panel pre {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.75rem;
  overflow-x: auto;
}
.output-panel code {
  font-family: var(--mono);
  background: var(--surface-2);
  padding: 0.1rem 0.35rem;
  border-radius: 5px;
  font-size: 0.9em;
}
.output-panel pre code { background: none; padding: 0; }
.output-panel blockquote {
  margin: 0.75rem 0;
  padding: 0.25rem 0.9rem;
  border-left: 3px solid var(--accent);
  color: var(--text-muted);
}
.output-panel a { color: var(--accent); }

/* Word-level diff */
.diff-add { background: rgba(31, 157, 85, 0.22); text-decoration: none; }
.diff-del { background: rgba(214, 69, 69, 0.22); text-decoration: line-through; }
.diff-line-add { background: rgba(31, 157, 85, 0.12); display: block; }
.diff-line-del { background: rgba(214, 69, 69, 0.12); display: block; }

/* Regex match highlight */
.output-panel mark, .regex-mark {
  background: var(--accent-soft);
  color: var(--accent);
  border-radius: 3px;
  padding: 0 0.1rem;
}

/* Key/value output list (Case Converter, String Escape) */
.kv-list { display: flex; flex-direction: column; gap: 0.6rem; margin-top: 1.25rem; }
.kv-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.55rem 0.75rem;
}
.kv-row .kv-label {
  flex: 0 0 140px;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
}
.kv-row .kv-value {
  flex: 1;
  font-family: var(--mono);
  font-size: 0.9rem;
  overflow-x: auto;
  white-space: pre;
}
.kv-row .copy-btn {
  position: static;
  flex: 0 0 auto;
}

.checkbox-row { display: flex; align-items: center; gap: 0.4rem; }
.checkbox-row input[type="checkbox"] { width: auto; }
.checkbox-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 0.6rem 1rem;
  margin-top: 1rem;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--border);
  background: var(--surface);
  margin-top: 2rem;
}
.footer-inner {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
  padding: 1.25rem;
  color: var(--text-muted);
  font-size: 0.85rem;
}

@media (max-width: 540px) {
  .hero h1 { font-size: 1.8rem; }
  .header-inner { height: 54px; }
}