:root {
  --ink:        #0F1117;
  --ink-soft:   #2A2D38;
  --muted:      #6B7280;
  --muted-2:    #9CA3AF;
  --line:       #E5E7EB;
  --line-soft:  #F3F4F6;
  --paper:      #FAFAF9;
  --paper-2:    #F0EFF9;
  --card:       #FFFFFF;

  --accent:     #4338CA;
  --accent-2:   #5B52D6;
  --accent-soft:#EDE9FE;

  --gold:       #B07D2B;
  --gold-soft:  #FBF1DC;

  --good:       #1F6B4A;
  --good-soft:  #E2EFE8;
  --warn:       #8A6A12;
  --warn-soft:  #FBF1DC;
  --bad:        #9A2A2A;
  --bad-soft:   #F6E3E3;

  --font-display: 'Fraunces', Georgia, serif;
  --font-body:    'Geist', -apple-system, system-ui, sans-serif;
  --font-mono:    'JetBrains Mono', ui-monospace, monospace;
  --font-heb:     'Heebo', 'Geist', sans-serif;
}

* { box-sizing: border-box; -webkit-font-smoothing: antialiased; }
html, body { margin: 0; padding: 0; }

body {
  font-family: var(--font-body);
  color: var(--ink);
  background:
    radial-gradient(900px 500px at 100% -10%, #EDE9FE 0%, transparent 60%),
    radial-gradient(800px 400px at -10% 110%, #F0EFF9 0%, transparent 55%),
    var(--paper);
  min-height: 100vh;
  padding: env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left);
}

.app {
  max-width: 560px;
  margin: 0 auto;
  padding: 16px 18px 32px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  min-height: 100vh;
}

/* ===== Header ===== */
.app-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 0 4px;
}
.brand { display: flex; align-items: center; gap: 10px; }
.logo {
  width: 36px; height: 36px;
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 2px 8px rgba(67,56,202,0.28);
}
.logo img, .logo svg {
  width: 36px; height: 36px;
  border-radius: 10px;
  display: block;
}
.brand-name {
  font: 600 16px/1 var(--font-body);
  letter-spacing: -0.01em;
  color: var(--ink);
}
.brand-name span { color: var(--muted); font-weight: 400; }

.lang-dropdown {
  position: relative;
  display: inline-block;
}
.lang-trigger {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 5px 9px;
  font: 500 11px/1 var(--font-body);
  color: var(--ink-soft);
  cursor: pointer;
  transition: all 0.15s ease;
}
.lang-trigger:hover {
  border-color: var(--accent);
  color: var(--accent);
}
.lang-menu {
  position: absolute;
  bottom: calc(100% + 6px);
  right: 0;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 10px;
  box-shadow: 0 4px 16px rgba(15,20,25,0.12);
  padding: 5px;
  list-style: none;
  margin: 0;
  min-width: 130px;
  z-index: 100;
}
.lang-menu li {
  padding: 8px 12px;
  border-radius: 7px;
  font: 400 12px/1 var(--font-body);
  color: var(--ink-soft);
  cursor: pointer;
  transition: background 0.12s;
}
.lang-menu li:hover { background: var(--paper-2); color: var(--ink); }
.lang-menu li.active { color: var(--accent); font-weight: 600; }

/* ===== Mode toggle ===== */
.mode-toggle {
  background: var(--paper-2);
  border-radius: 14px;
  padding: 5px;
  display: flex;
  gap: 3px;
}
.mode-toggle button {
  flex: 1;
  border: 0;
  background: transparent;
  padding: 12px 0;
  border-radius: 10px;
  font: 500 13px/1 var(--font-body);
  color: var(--ink-soft);
  cursor: pointer;
  letter-spacing: -0.005em;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  transition: all 0.16s ease;
}
.mode-toggle button.active {
  background: var(--card);
  color: var(--ink);
  box-shadow: 0 1px 4px rgba(15,20,25,0.08);
}
.mode-toggle button svg { opacity: 0.7; }
.mode-toggle button.active svg { opacity: 1; color: var(--accent); }

/* ===== Input area ===== */
.input-area {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 16px;
}
.input-block { display: flex; flex-direction: column; }
.math-preview {
  margin-top: 8px;
  padding: 10px 14px;
  background: var(--paper);
  border: 1px solid var(--accent);
  border-radius: 10px;
  font-size: 15px;
  line-height: 1.6;
  color: var(--ink);
  overflow-x: auto;
}
.math-preview.hidden { display: none; }
.input-label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 8px;
}
textarea {
  width: 100%;
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: 12px;
  padding: 12px 14px;
  font: 400 15px/1.5 var(--font-body);
  color: var(--ink);
  resize: vertical;
  outline: none;
  transition: border-color 0.16s ease;
  font-family: var(--font-body);
}
textarea:focus {
  border-color: var(--accent);
  background: white;
}
textarea[dir="rtl"] {
  direction: rtl;
  font-family: var(--font-heb);
}

.examples {
  display: flex;
  gap: 6px;
  margin-top: 10px;
  overflow-x: auto;
  scrollbar-width: none;
  padding-bottom: 2px;
}
.examples::-webkit-scrollbar { display: none; }
.ex-chip {
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: 999px;
  padding: 6px 11px;
  font: 500 11px/1 var(--font-body);
  color: var(--ink-soft);
  white-space: nowrap;
  cursor: pointer;
  letter-spacing: -0.005em;
  flex-shrink: 0;
}
.ex-chip:hover, .ex-chip:active {
  border-color: var(--accent);
  color: var(--accent);
}

.level-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-top: 14px;
}
.level-label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted);
  flex-shrink: 0;
}
.level-seg {
  flex: 1;
  display: flex;
  gap: 3px;
  background: var(--paper-2);
  border-radius: 8px;
  padding: 3px;
}
.level-seg button {
  flex: 1;
  min-width: 0;
  border: 0;
  background: transparent;
  padding: 7px 2px;
  border-radius: 6px;
  font: 500 10px/1 var(--font-body);
  color: var(--ink-soft);
  cursor: pointer;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  text-align: center;
}
.level-seg button.active {
  background: white;
  color: var(--ink);
  box-shadow: 0 1px 2px rgba(15,20,25,0.06);
}

.primary-btn {
  margin-top: 14px;
  width: 100%;
  background: linear-gradient(135deg, #4338CA 0%, #6D28D9 100%);
  color: white;
  border: 0;
  border-radius: 12px;
  padding: 14px 16px;
  font: 500 15px/1 var(--font-body);
  letter-spacing: -0.005em;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  transition: all 0.18s ease;
  box-shadow: 0 2px 10px rgba(67,56,202,0.32);
}
.primary-btn:hover {
  background: linear-gradient(135deg, #5B52D6 0%, #7C3AED 100%);
  transform: translateY(-1px);
  box-shadow: 0 4px 16px rgba(67,56,202,0.38);
}
.primary-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

/* ===== Status / errors ===== */
.status-bar {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 14px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  font: 500 13px/1 var(--font-body);
  color: var(--ink-soft);
}
.spinner {
  width: 18px; height: 18px;
  border: 2px solid var(--line);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

.error-bar {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 14px;
  background: var(--bad-soft);
  border: 1px solid #E9C8C8;
  border-radius: 12px;
  font: 500 13px/1.4 var(--font-body);
  color: var(--bad);
}

/* ===== Result ===== */
.result { display: flex; flex-direction: column; gap: 12px; }

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--accent);
  background: var(--accent-soft);
  padding: 5px 9px;
  border-radius: 6px;
  width: fit-content;
}
.tag .dot {
  width: 5px; height: 5px;
  border-radius: 50%;
  background: var(--accent-2);
}

.verified {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 11px 14px;
  background: var(--good-soft);
  border-radius: 12px;
  font: 500 13px/1.3 var(--font-body);
  color: var(--good);
}
.verified .v-icon {
  width: 22px; height: 22px;
  border-radius: 50%;
  background: var(--good);
  color: white;
  display: grid;
  place-items: center;
  flex-shrink: 0;
}
.verified .v-sub {
  font-weight: 400;
  color: var(--ink-soft);
  opacity: 0.8;
  font-size: 11px;
  margin-top: 2px;
}

.step {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 14px 16px;
}
.step .top {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 10px;
}
.step .num {
  width: 24px; height: 24px;
  border-radius: 7px;
  background: var(--ink);
  color: white;
  font: 600 12px/1 var(--font-mono);
  display: grid;
  place-items: center;
  flex-shrink: 0;
}
.step .title {
  font: 500 14px/1.35 var(--font-body);
  color: var(--ink);
  letter-spacing: -0.005em;
  flex: 1;
}
.step .math {
  padding: 10px 12px;
  background: var(--paper-2);
  border-radius: 10px;
  font-size: 15px;
  overflow-x: auto;
}
.step .reasoning {
  margin-top: 10px;
  padding: 10px 12px;
  background: var(--accent-soft);
  border-radius: 10px;
  font: 400 13px/1.55 var(--font-body);
  color: var(--ink-soft);
  border-left: 2px solid var(--accent-2);
}
.step .reasoning b {
  color: var(--accent);
  font-weight: 600;
  text-transform: uppercase;
  font-size: 10px;
  letter-spacing: 0.14em;
  display: block;
  margin-bottom: 4px;
  font-family: var(--font-mono);
}

.final {
  background: linear-gradient(135deg, #1E1B4B 0%, #312E81 100%);
  color: white;
  border-radius: 16px;
  padding: 18px 20px;
  position: relative;
  overflow: hidden;
}
.final::before {
  content: "";
  position: absolute;
  top: -40px; right: -40px;
  width: 140px; height: 140px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(109,40,217,0.55) 0%, transparent 70%);
}
.final .label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  opacity: 0.6;
  margin-bottom: 8px;
  position: relative;
}
.final .ans {
  font: 400 20px/1.3 var(--font-display);
  letter-spacing: -0.01em;
  position: relative;
  overflow-wrap: break-word;
  word-break: break-word;
}
.final .ans .katex { color: white !important; }

.math-display { margin: 6px 0; overflow-x: auto; }
.math-prose   { margin: 4px 0; }

.alternatives {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 12px 14px;
}
.alternatives .alt-label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 8px;
}
.alternatives ul {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.alternatives li {
  font: 400 13px/1.5 var(--font-body);
  color: var(--ink-soft);
  padding-left: 16px;
  position: relative;
  letter-spacing: -0.003em;
}
.alternatives li::before {
  content: "→";
  position: absolute;
  left: 0;
  color: var(--accent-2);
  font-weight: 500;
}

.followup {
  background: var(--gold-soft);
  border: 1px solid #ECDFC0;
  border-radius: 12px;
  padding: 12px 14px;
}
.followup .fu-label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 6px;
}
.followup .fu-q {
  font: 400 14px/1.45 var(--font-body);
  color: var(--ink);
  letter-spacing: -0.005em;
}
.followup .fu-try-btn {
  margin-top: 10px;
  padding: 5px 12px;
  background: transparent;
  border: 1px solid var(--gold);
  border-radius: 6px;
  font: 500 11px/1 var(--font-mono);
  color: var(--gold);
  cursor: pointer;
  letter-spacing: 0.04em;
  transition: background 0.15s, color 0.15s;
  display: inline-block;
}
.followup .fu-try-btn:hover {
  background: var(--gold);
  color: #fff;
}

/* ===== Check My Work ===== */
.cmw-banner {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
}
.cmw-banner .summary { flex: 1; }
.cmw-banner .sum-label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted);
}
.cmw-banner .sum-text {
  font: 500 13px/1.4 var(--font-body);
  color: var(--ink);
  margin-top: 3px;
  letter-spacing: -0.005em;
}
.cmw-banner .score-ring {
  width: 50px; height: 50px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  flex-shrink: 0;
}
.cmw-banner .score-ring .inner {
  width: 40px; height: 40px;
  border-radius: 50%;
  background: var(--card);
  display: grid;
  place-items: center;
  font: 600 13px/1 var(--font-mono);
  color: var(--ink);
}

.cmw-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}
.cmw-tag {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--bad);
  background: var(--bad-soft);
  padding: 4px 9px;
  border-radius: 5px;
}

.a-step {
  border-radius: 12px;
  padding: 12px 14px;
  border: 1px solid;
}
.a-step.ok   { background: var(--good-soft); border-color: #C3DCCB; }
.a-step.warn { background: var(--warn-soft); border-color: #ECDFC0; }
.a-step.bad  { background: var(--bad-soft);  border-color: #E9C8C8; }
.a-step .head {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 8px;
}
.a-step .badge {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  padding: 4px 7px;
  border-radius: 5px;
  font-weight: 500;
}
.a-step.ok   .badge { background: var(--good); color: white; }
.a-step.warn .badge { background: var(--warn); color: white; }
.a-step.bad  .badge { background: var(--bad);  color: white; }
.a-step .num {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--muted);
  letter-spacing: 0.06em;
}
.a-step .your-line {
  padding: 8px 10px;
  background: rgba(255,255,255,0.6);
  border-radius: 8px;
  font-size: 14px;
  overflow-x: auto;
}
.a-step .explain {
  margin-top: 8px;
  font: 400 13px/1.55 var(--font-body);
  color: var(--ink-soft);
  letter-spacing: -0.003em;
}
.a-step .explain b {
  font-weight: 600;
  color: var(--ink);
}
.a-step .fix {
  margin-top: 8px;
  padding: 8px 10px;
  background: white;
  border: 1px dashed var(--good);
  border-radius: 8px;
  font-size: 13px;
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}
.a-step .fix .fix-label {
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--good);
  flex-shrink: 0;
}

/* ===== History ===== */
.history-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}
.history-count {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  color: var(--muted-2);
}
.history-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
  min-height: 60px;
}
.history-spinner {
  display: flex;
  justify-content: center;
  padding: 20px 0;
}
.history-empty {
  flex-direction: column;
  align-items: center;
  gap: 10px;
  padding: 28px 0 12px;
  color: var(--muted);
  font: 400 13px/1.5 var(--font-body);
  text-align: center;
}
.history-error {
  font: 400 13px/1 var(--font-body);
  color: var(--bad);
  text-align: center;
  padding: 16px 0;
  margin: 0;
}
.history-card {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 11px 13px;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s, transform 0.12s;
}
.history-card:hover {
  border-color: var(--accent-2);
  background: var(--card);
  transform: translateY(-1px);
}
.hc-top {
  display: flex;
  align-items: center;
  gap: 7px;
  margin-bottom: 7px;
  flex-wrap: wrap;
}
.hc-mode {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  padding: 3px 7px;
  border-radius: 4px;
  font-weight: 500;
}
.hc-mode.solve {
  background: var(--accent-soft);
  color: var(--accent);
}
.hc-mode.check {
  background: var(--gold-soft);
  color: var(--gold);
}
.hc-tag {
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.1em;
  color: var(--muted);
  text-transform: uppercase;
}
.hc-score {
  font-family: var(--font-mono);
  font-size: 10px;
  font-weight: 600;
  color: var(--good);
  background: var(--good-soft);
  padding: 2px 6px;
  border-radius: 4px;
}
.hc-time {
  font-family: var(--font-mono);
  font-size: 9px;
  color: var(--muted-2);
  margin-left: auto;
}
.hc-problem {
  font: 400 13px/1.45 var(--font-body);
  color: var(--ink-soft);
  overflow: hidden;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  letter-spacing: -0.003em;
}

/* ── History accordion ── */
.history-card { position: relative; }
.history-card.hc-open { border-color: var(--accent-2); }

.hc-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 6px;
}
.hc-header-left  { display: flex; align-items: center; gap: 7px; flex-wrap: wrap; }
.hc-header-right { display: flex; align-items: center; gap: 6px; flex-shrink: 0; }

.hc-pdf-btn {
  background: none;
  border: none;
  padding: 3px;
  border-radius: 4px;
  cursor: pointer;
  color: var(--muted);
  line-height: 0;
  transition: color 0.15s, background 0.15s;
}
.hc-pdf-btn:hover { color: var(--accent); background: var(--accent-soft); }

.hc-chevron {
  font-size: 8px;
  color: var(--muted-2);
  transition: transform 0.2s;
  user-select: none;
}
.history-card.hc-open .hc-chevron { transform: rotate(180deg); }

.hc-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease, padding 0.2s;
}
.history-card.hc-open .hc-body {
  max-height: 9999px;
  padding-top: 12px;
  border-top: 1px solid var(--line);
  margin-top: 10px;
}

.hc-actions {
  display: flex;
  gap: 8px;
  margin-top: 14px;
  padding-top: 12px;
  border-top: 1px solid var(--line);
  flex-wrap: wrap;
}
.hc-action-btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 6px 14px;
  border-radius: 7px;
  border: 1px solid var(--line);
  background: var(--paper);
  color: var(--ink-soft);
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s, color 0.15s;
}
.hc-action-btn:hover { border-color: var(--accent-2); background: var(--accent-soft); color: var(--accent); }

.hc-no-solution {
  font-size: 12px;
  color: var(--muted-2);
  font-style: italic;
  padding: 8px 0;
  margin: 0;
}

/* RTL */
[dir="rtl"], .he { font-family: var(--font-heb); }
.step.he .title, .step.he .reasoning { direction: rtl; text-align: right; }
.cmw-banner.he .sum-text { direction: rtl; text-align: right; font-family: var(--font-heb); }
.a-step.he { direction: rtl; text-align: right; font-family: var(--font-heb); }
.followup.he .fu-q { direction: rtl; text-align: right; font-family: var(--font-heb); }

/* ===== Bonus / Promo Card ===== */
.bonus-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  overflow: hidden;
  transition: border-color 0.2s;
}
.bonus-card:focus-within { border-color: var(--accent); }

.bonus-toggle {
  width: 100%;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 13px 16px;
  background: transparent;
  border: none;
  cursor: pointer;
  text-align: left;
  transition: background 0.15s;
}
.bonus-toggle:hover { background: var(--paper-2); }

.bonus-toggle-icon {
  width: 28px; height: 28px;
  border-radius: 8px;
  background: var(--accent-soft);
  display: grid;
  place-items: center;
  flex-shrink: 0;
  color: var(--accent);
}
.bonus-toggle-label {
  flex: 1;
  font: 500 13px/1 var(--font-body);
  color: var(--ink-soft);
  letter-spacing: -0.005em;
}
.bonus-chevron {
  color: var(--muted-2);
  transition: transform 0.25s cubic-bezier(0.4,0,0.2,1);
  flex-shrink: 0;
}
.bonus-toggle.open .bonus-chevron { transform: rotate(180deg); }

.bonus-body {
  padding: 0 16px 16px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.bonus-body.hidden { display: none !important; }

.bonus-input-row { display: flex; flex-direction: column; gap: 8px; }

.bonus-input {
  flex: 1;
  min-width: 0;
  min-height: 44px;
  border: 1.5px solid var(--line);
  background: var(--paper);
  border-radius: 10px;
  padding: 10px 13px;
  font: 500 13px/1 var(--font-mono);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink);
  outline: none;
  transition: border-color 0.16s;
}
.bonus-input:focus {
  border-color: var(--accent);
  background: white;
}
.bonus-input::placeholder {
  text-transform: none;
  font-weight: 400;
  letter-spacing: 0;
  color: var(--muted-2);
}
.bonus-apply {
  padding: 12px 16px;
  background: linear-gradient(135deg, #4338CA 0%, #6D28D9 100%);
  color: white;
  border: none;
  border-radius: 10px;
  font: 600 11px/1 var(--font-mono);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  cursor: pointer;
  width: 100%;
  transition: opacity 0.15s;
}
.bonus-apply:hover { opacity: 0.88; }

.bonus-msg {
  margin: 0;
  font: 400 12px/1.4 var(--font-body);
  color: var(--muted);
}
.bonus-msg.success { color: var(--good); }
.bonus-msg.error   { color: var(--bad); }

/* ===== Footer ===== */
.app-foot {
  margin-top: auto;
  background: linear-gradient(160deg, #18172A 0%, #0E0D1A 100%);
  border-radius: 20px;
  padding: 28px 24px 20px;
  color: rgba(255,255,255,0.85);
  font-family: var(--font-body);
  overflow: visible;
  position: relative;
}
.app-foot::before {
  content: "";
  position: absolute;
  top: -60px; right: -60px;
  width: 200px; height: 200px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(109,40,217,0.25) 0%, transparent 70%);
  pointer-events: none;
}

.foot-top { display: flex; flex-direction: column; gap: 6px; }
.foot-wordmark { display: flex; align-items: center; gap: 8px; }
.foot-wordmark-text {
  font: 600 15px/1 var(--font-body);
  color: #fff;
  letter-spacing: -0.01em;
}
.foot-version {
  font: 500 9px/1 var(--font-mono);
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: rgba(255,255,255,0.3);
}
.foot-desc {
  font: 400 11.5px/1.65 var(--font-body);
  color: rgba(255,255,255,0.42);
  margin: 8px 0 0;
  max-width: 460px;
}

.foot-divider {
  height: 1px;
  background: rgba(255,255,255,0.08);
  margin: 16px 0;
}

.foot-nav { display: flex; flex-wrap: wrap; gap: 4px 16px; align-items: center; }
.foot-nav a {
  font: 500 10px/1 var(--font-mono);
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: rgba(255,255,255,0.45);
  text-decoration: none;
  transition: color 0.15s;
  padding: 4px 0;
}
.foot-nav a:hover { color: rgba(255,255,255,0.9); }

.foot-controls {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-top: 10px;
}
.foot-controls .lang-trigger {
  background: rgba(255,255,255,0.08);
  border-color: rgba(255,255,255,0.12);
  color: rgba(255,255,255,0.65);
}
.foot-controls .lang-trigger:hover {
  background: rgba(255,255,255,0.14);
  border-color: rgba(255,255,255,0.25);
  color: rgba(255,255,255,0.9);
}
.foot-controls .lang-menu {
  background: #1E1B4B;
  border-color: rgba(255,255,255,0.12);
  box-shadow: 0 -4px 24px rgba(0,0,0,0.5);
  max-width: 170px;
  left: 0;
  right: auto;
  z-index: 1000;
}
/* RTL support (Hebrew) — flip dropdown anchor */
[dir="rtl"] .lang-menu {
  right: auto;
  left: 0;
}
[dir="rtl"] .foot-controls .lang-menu {
  right: 0;
  left: auto;
}
.foot-controls .lang-menu li { color: rgba(255,255,255,0.6); }
.foot-controls .lang-menu li:hover { background: rgba(255,255,255,0.08); color: #fff; }
.foot-controls .lang-menu li.active { color: #A78BFA; }

.foot-controls .ai-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font: 500 10px/1 var(--font-mono);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: rgba(255,255,255,0.38);
  background: rgba(255,255,255,0.06);
  border: 1px solid rgba(255,255,255,0.08);
  padding: 5px 9px;
  border-radius: 8px;
}

.foot-legal { display: flex; flex-direction: column; gap: 3px; }
.foot-legal p {
  margin: 0;
  font: 400 10px/1.5 var(--font-body);
  color: rgba(255,255,255,0.3);
}
.foot-legal strong { color: rgba(255,255,255,0.45); font-weight: 500; }
.foot-legal .trademark { font-size: 9px; color: rgba(255,255,255,0.22); }

.disclaimer-note {
  margin: 4px 0 0;
  font: 400 10px/1.55 var(--font-body);
  color: rgba(255,255,255,0.2);
}

/* ===== Math sub-tabs ===== */
.math-subtab-bar {
  display: flex;
  gap: 4px;
  padding: 0 2px 8px;
  overflow-x: auto;
  scrollbar-width: none;
  flex-wrap: nowrap;
}
.math-subtab-bar::-webkit-scrollbar { display: none; }
.math-subtab-btn {
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: 7px;
  padding: 5px 11px;
  font: 500 11px/1 var(--font-body);
  color: var(--ink-soft);
  cursor: pointer;
  white-space: nowrap;
  flex-shrink: 0;
  transition: border-color 0.14s ease, background 0.14s ease, color 0.14s ease;
  letter-spacing: -0.01em;
}
.math-subtab-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-soft);
}
.math-subtab-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  box-shadow: 0 1px 4px rgba(67,56,202,0.25);
}

/* Animations */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(6px); }
  to   { opacity: 1; transform: translateY(0); }
}
.result > * { animation: fadeUp 0.32s ease both; }
.result > *:nth-child(2) { animation-delay: 0.05s; }
.result > *:nth-child(3) { animation-delay: 0.10s; }
.result > *:nth-child(4) { animation-delay: 0.15s; }
.result > *:nth-child(5) { animation-delay: 0.20s; }
.result > *:nth-child(6) { animation-delay: 0.25s; }
.result > *:nth-child(7) { animation-delay: 0.30s; }
.result > *:nth-child(8) { animation-delay: 0.35s; }
.result > *:nth-child(9) { animation-delay: 0.40s; }
.result > *:nth-child(10) { animation-delay: 0.45s; }

.hidden { display: none !important; }

@media (min-width: 720px) {
  .app { max-width: 640px; padding: 32px 24px; }
  .app-head { padding: 0 0 8px; }
}

/* ===== Stripe credit packages ===== */
.pkg-list {
  display: flex;
  gap: 8px;
  margin: 12px 0 8px;
}
.pkg-btn {
  flex: 1;
  border: 1.5px solid var(--line);
  background: var(--paper);
  border-radius: 12px;
  padding: 12px 8px;
  cursor: pointer;
  text-align: center;
  transition: all 0.16s ease;
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.pkg-btn:hover { border-color: var(--accent); background: var(--accent-soft); }
.pkg-btn.loading { opacity: 0.6; pointer-events: none; }
.pkg-name { font: 600 12px/1 var(--font-body); color: var(--ink); }
.pkg-credits { font: 400 11px/1 var(--font-mono); color: var(--muted); }
.pkg-price { font: 700 15px/1 var(--font-body); color: var(--accent); margin-top: 2px; }

/* Payment toast */
.payment-toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--ink);
  color: white;
  padding: 12px 20px;
  border-radius: 12px;
  font: 500 13px/1.4 var(--font-body);
  display: flex;
  align-items: center;
  gap: 8px;
  z-index: 9999;
  box-shadow: 0 4px 20px rgba(0,0,0,0.2);
  animation: slideUp 0.2s ease;
}
.payment-toast.success { background: var(--good); }
@keyframes slideUp {
  from { opacity: 0; transform: translateX(-50%) translateY(10px); }
  to   { opacity: 1; transform: translateX(-50%) translateY(0); }
}

/* ===== Function Plot ===== */
.s2s-plot {
  margin: 20px 0 8px;
  border-radius: 10px;
  overflow: hidden;
  background: #fafaf8;
  border: 1px solid var(--border, #e5e7eb);
}
.s2s-plot svg { display: block; }
.s2s-plot .top-right-legend { display: none; }