:root {
  --bg: #0f1420;
  --bg-elevated: #161c2c;
  --panel: #1a2133;
  --border: #2a3350;
  --text: #e8ecf6;
  --text-dim: #9aa4bf;
  --accent: #6c8cff;
  --accent-soft: rgba(108, 140, 255, 0.14);
  --accent-solid: #4a67e8; /* button fill: white text passes 4.5:1 */
  --accent-solid-hover: #3f5bd9;
  --accent-strong-text: #8ea6ff;
  --dash: #64729e; /* dashed drop-zone border: 3.4:1 on panel */
  --good: #4fd1a5;
  --warn: #ffb86c;
  --danger: #ff6b81;
  --radius: 12px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

/* Visible keyboard focus everywhere */
:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ---------- Header + hero ---------- */
.site-header {
  max-width: 920px;
  margin: 0 auto;
  padding: 1.25rem 1.5rem 0;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  color: var(--text);
  text-decoration: none;
  border-radius: 8px;
}

.brand-mark {
  background: var(--accent-soft);
  color: var(--accent);
  width: 2rem;
  height: 2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
}

.brand-name {
  font-size: 0.98rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.hero {
  max-width: 760px;
  margin: 0 auto;
  padding: 3rem 1.5rem 2rem;
  text-align: center;
}

.hero h1 {
  margin: 0;
  color: #fff;
  font-size: clamp(1.9rem, 5.2vw, 3.1rem);
  line-height: 1.12;
  letter-spacing: -0.03em;
  font-weight: 700;
}

.hero-sub {
  color: var(--text-dim);
  margin: 1rem auto 0;
  max-width: 560px;
  font-size: clamp(1rem, 2.2vw, 1.12rem);
  line-height: 1.5;
}

.layout {
  max-width: 920px;
  margin: 0 auto;
  padding: 0 1.5rem 3rem;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
}

.panel.hidden { display: none; }

/* ---------- Drop zone ---------- */
.dropzone {
  border: 2px dashed var(--dash);
  border-radius: var(--radius);
  padding: 2.25rem 1.5rem 1.75rem;
  text-align: center;
  cursor: pointer;
  transition: border-color 0.15s ease, background-color 0.15s ease;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.dropzone:hover {
  border-color: var(--accent);
}

.dropzone:focus-visible {
  border-color: var(--accent);
  border-style: solid;
  outline-offset: 3px;
}

.dropzone.dragover {
  border-color: var(--accent);
  border-style: solid;
  background: var(--accent-soft);
  box-shadow: 0 0 0 4px rgba(108, 140, 255, 0.18);
}

.dropzone-icon {
  color: var(--accent);
  margin-bottom: 1rem;
}

.choose-btn {
  font-size: 0.98rem;
  padding: 0.7rem 1.5rem;
}

.dropzone-text {
  color: var(--text-dim);
  font-size: 0.92rem;
  line-height: 1.5;
  margin: 0.85rem 0 0;
}

.dropzone-hint {
  color: var(--text-dim);
  font-size: 0.8rem;
  margin: 0.4rem 0 0;
}

.link-btn {
  background: none;
  border: none;
  padding: 0;
  font: inherit;
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 2px;
  cursor: pointer;
  border-radius: 3px;
}

.link-btn:hover { color: var(--accent-strong-text); }

.dropzone-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem 1rem;
  flex-wrap: wrap;
  margin-top: 1rem;
}

.privacy-note {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  margin: 0;
  color: var(--text-dim);
  font-size: 0.85rem;
}

.privacy-note svg { color: var(--good); flex-shrink: 0; }

.status-line {
  margin-top: 0.9rem;
  font-size: 0.85rem;
  color: var(--text-dim);
}

.status-line:empty { display: none; }

.status-line.error { color: var(--danger); }
.status-line.good { color: var(--good); }

.panel-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.3rem;
}

.panel-header h2 {
  font-size: 1.05rem;
  margin: 0;
}

.panel-sub {
  color: var(--text-dim);
  font-size: 0.85rem;
  margin: 0.3rem 0 1rem;
}

.ghost-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 0.4rem 0.8rem;
  border-radius: 8px;
  cursor: pointer;
  font-size: 0.8rem;
}

.ghost-btn:hover { color: var(--text); border-color: var(--text-dim); }

.file-group-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.8rem;
  max-height: 420px;
  overflow-y: auto;
}

.file-group {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.7rem 0.9rem;
}

.file-group-header {
  display: flex;
  align-items: center;
  gap: 0.7rem;
  margin-bottom: 0.4rem;
}

.file-group-name {
  flex: 1;
  font-size: 0.88rem;
  font-weight: 600;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.sheet-sublist {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.sheet-row {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.35rem 0.5rem;
  border-radius: 8px;
}

.sheet-row:hover { background: rgba(255,255,255,0.03); }

.sheet-row input[type="checkbox"] {
  width: 1.05rem;
  height: 1.05rem;
  accent-color: var(--accent);
  flex-shrink: 0;
}

.sheet-row .sheet-label {
  font-size: 0.85rem;
  flex-shrink: 0;
  min-width: 60px;
}

.sheet-row .header-preview {
  font-size: 0.78rem;
  color: var(--text-dim);
  flex: 1;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.source-meta {
  font-size: 0.78rem;
  color: var(--text-dim);
  flex-shrink: 0;
}

.remove-btn {
  background: none;
  border: none;
  color: var(--text-dim);
  cursor: pointer;
  font-size: 0.9rem;
  padding: 0.2rem 0.4rem;
  flex-shrink: 0;
}

.remove-btn:hover { color: var(--danger); }

.badge {
  font-size: 0.72rem;
  padding: 0.15rem 0.5rem;
  border-radius: 999px;
  flex-shrink: 0;
}

.badge-warn {
  background: rgba(255, 184, 108, 0.15);
  color: var(--warn);
}

.header-comparison {
  font-size: 0.85rem;
}

.comparison-ok {
  color: var(--good);
  margin: 0 0 0.3rem;
}

.comparison-summary {
  color: var(--text-dim);
  margin: 0 0 0.5rem;
}

.diff-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}

.diff-list li {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.4rem 0.7rem;
  font-size: 0.85rem;
}

.controls-row {
  display: flex;
  gap: 1.2rem;
  margin-top: 1.1rem;
  flex-wrap: wrap;
}

.strategy-fieldset, .source-cols-fieldset {
  flex: 1;
  min-width: 220px;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.7rem 0.9rem;
}

.strategy-fieldset legend, .source-cols-fieldset legend {
  font-size: 0.78rem;
  color: var(--text-dim);
  padding: 0 0.3rem;
}

.strategy-row, .checkbox-row {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 0.5rem;
  font-size: 0.85rem;
  padding: 0.3rem 0;
  cursor: pointer;
}

.strategy-row input, .checkbox-row input {
  accent-color: var(--accent);
  flex-shrink: 0;
}

.checkbox-row code {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.05rem 0.35rem;
  font-size: 0.8rem;
}

.single-sheet-note {
  color: var(--warn);
  font-size: 0.85rem;
  margin: 0.3rem 0 0;
}

.single-sheet-note.hidden { display: none; }

.summary-chips {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.chip {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  color: var(--text-dim);
  font-size: 0.78rem;
  padding: 0.3rem 0.7rem;
  border-radius: 999px;
}

.chip strong { color: var(--text); }

.table-scroll {
  overflow: auto;
  max-height: 420px;
  border: 1px solid var(--border);
  border-radius: 10px;
  margin-top: 0.9rem;
}

table {
  border-collapse: collapse;
  width: 100%;
  font-size: 0.82rem;
}

table th, table td {
  padding: 0.5rem 0.7rem;
  border-bottom: 1px solid var(--border);
  text-align: left;
  white-space: nowrap;
}

table th {
  background: var(--bg-elevated);
  color: var(--text-dim);
  position: sticky;
  top: 0;
  font-weight: 600;
}

table tr:hover td { background: rgba(255,255,255,0.02); }

.preview-note {
  color: var(--text-dim);
  font-size: 0.8rem;
  margin: 0.6rem 0 0;
}

.export-row {
  display: flex;
  gap: 0.6rem;
  margin-top: 1.2rem;
  flex-wrap: wrap;
}

#output-name {
  flex: 1;
  min-width: 160px;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 0.6rem 0.9rem;
  border-radius: 8px;
  font-size: 0.88rem;
}

.primary-btn, .secondary-btn {
  padding: 0.6rem 1.1rem;
  border-radius: 8px;
  font-size: 0.88rem;
  font-weight: 500;
  cursor: pointer;
  border: 1px solid transparent;
}

.primary-btn {
  background: var(--accent-solid);
  color: #fff;
}

.primary-btn:hover { background: var(--accent-solid-hover); }

.secondary-btn {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  color: var(--text);
}

.secondary-btn:hover { border-color: var(--text-dim); }

.primary-btn:disabled, .secondary-btn:disabled { opacity: 0.6; cursor: progress; }

/* ---------- Below the fold ---------- */
.content {
  max-width: 920px;
  margin: 0 auto;
  padding: 1.5rem 1.5rem 1rem;
  display: flex;
  flex-direction: column;
  gap: 3.5rem;
}

.content h2 {
  font-size: 1.5rem;
  letter-spacing: -0.02em;
  margin: 0 0 1.25rem;
  text-align: center;
}

.steps {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.step {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
}

.step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.9rem;
  height: 1.9rem;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent-strong-text);
  font-weight: 700;
  font-size: 0.9rem;
}

.step h3 {
  font-size: 1rem;
  margin: 0.8rem 0 0.35rem;
}

.step p {
  margin: 0;
  color: var(--text-dim);
  font-size: 0.9rem;
  line-height: 1.5;
}

.audience {
  text-align: center;
  color: var(--text-dim);
  max-width: 620px;
  margin: 1.5rem auto 0;
  line-height: 1.6;
}

.audience strong { color: var(--text); font-weight: 600; }

.faq {
  max-width: 720px;
  width: 100%;
  margin: 0 auto;
}

.faq details {
  border: 1px solid var(--border);
  background: var(--panel);
  border-radius: 10px;
  margin-bottom: 0.6rem;
}

.faq summary {
  cursor: pointer;
  list-style: none;
  padding: 1rem 2.75rem 1rem 1.1rem;
  font-weight: 600;
  font-size: 0.97rem;
  position: relative;
  border-radius: 10px;
}

.faq summary::-webkit-details-marker { display: none; }

.faq summary::after {
  content: "";
  position: absolute;
  right: 1.15rem;
  top: 50%;
  width: 0.5rem;
  height: 0.5rem;
  border-right: 2px solid var(--accent);
  border-bottom: 2px solid var(--accent);
  transform: translateY(-70%) rotate(45deg);
  transition: transform 0.15s ease;
}

.faq details[open] summary::after { transform: translateY(-30%) rotate(-135deg); }

.faq summary:hover { color: #fff; }

.faq-body {
  padding: 0 1.1rem 1rem;
  color: var(--text-dim);
  font-size: 0.92rem;
  line-height: 1.6;
}

.faq-body p { margin: 0 0 0.6rem; }
.faq-body p:last-child { margin-bottom: 0; }

.faq-body code {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.05rem 0.35rem;
  font-size: 0.82rem;
  color: var(--text);
}

.site-footer {
  text-align: center;
  color: var(--text-dim);
  font-size: 0.8rem;
  padding: 2.5rem 1.5rem 2.5rem;
}

.site-footer p { margin: 0; }

/* ---------- Small screens ---------- */
@media (max-width: 680px) {
  .steps { grid-template-columns: 1fr; }
}

@media (max-width: 480px) {
  .site-header, .layout, .content { padding-left: 1rem; padding-right: 1rem; }
  .hero { padding: 2rem 1rem 1.5rem; }
  .panel { padding: 1rem; }
  .dropzone { padding: 1.75rem 1rem 1.5rem; }
  .dropzone-footer { flex-direction: column; align-items: stretch; text-align: center; }
  .privacy-note { justify-content: center; }
  .controls-row { flex-direction: column; }
  .strategy-fieldset, .source-cols-fieldset { min-width: 0; }
  .strategy-row .source-meta { flex-shrink: 1; }
  .sheet-row { flex-wrap: wrap; }
  .sheet-row .header-preview { flex-basis: 100%; padding-left: 1.65rem; }
  .export-row > * { flex: 1 1 100%; }
}