:root {
  --bg: #050914;
  --bg-soft: rgba(8, 18, 38, 0.72);
  --card: rgba(12, 29, 63, 0.74);
  --surface-strong: rgba(7, 19, 41, 0.72);
  --surface-soft: rgba(7, 19, 41, 0.62);
  --surface-hover: rgba(11, 30, 64, 0.78);
  --surface-elevated: rgba(14, 39, 80, 0.9);
  --active-card-end: rgba(7, 19, 41, 0.9);
  --input-bg: rgba(4, 14, 32, 0.95);
  --hero-panel-bg: rgba(8, 22, 45, 0.6);
  --overlay-bg: rgba(2, 8, 20, 0.72);
  --modal-bg: rgba(7, 20, 44, 0.96);
  --card-border-soft: rgba(142, 180, 255, 0.2);
  --card-border-strong: rgba(142, 180, 255, 0.35);
  --muted-strong: #95b5e8;
  --line: rgba(125, 181, 255, 0.22);
  --text: #e8f3ff;
  --text-soft: #95a8c8;
  --primary: #4ea3ff;
  --primary-strong: #2f86f5;
  --accent: #6ec8ff;
}

:root[data-theme="light"] {
  --bg: #edf4ff;
  --bg-soft: rgba(255, 255, 255, 0.82);
  --card: rgba(255, 255, 255, 0.86);
  --surface-strong: #f8fbff;
  --surface-soft: #f4f8ff;
  --surface-hover: #eaf2ff;
  --surface-elevated: #eef5ff;
  --active-card-end: #d9e8ff;
  --input-bg: #ffffff;
  --hero-panel-bg: #deecff;
  --overlay-bg: rgba(16, 35, 63, 0.28);
  --modal-bg: #ffffff;
  --card-border-soft: rgba(46, 112, 201, 0.2);
  --card-border-strong: rgba(46, 112, 201, 0.35);
  --muted-strong: #46658d;
  --line: rgba(46, 112, 201, 0.24);
  --text: #10233f;
  --text-soft: #516888;
  --primary: #2f86f5;
  --primary-strong: #1d6fd8;
  --accent: #1767c3;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  min-height: 100vh;
  font-family: "Segoe UI", "Roboto", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at 10% 12%, rgba(56, 130, 255, 0.23), transparent 34%),
    radial-gradient(circle at 90% 20%, rgba(20, 110, 255, 0.19), transparent 36%),
    radial-gradient(circle at 50% 95%, rgba(0, 74, 186, 0.18), transparent 42%),
    var(--bg);
  line-height: 1.5;
  padding: 22px;
}

.wrapper {
  width: min(1120px, 100%);
  margin: 0 auto;
}

.floating-nav {
  position: sticky;
  top: 16px;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 14px 20px;
  border-radius: 18px;
  border: 1px solid var(--line);
  background: var(--bg-soft);
  backdrop-filter: blur(16px);
  box-shadow: 0 15px 40px rgba(0, 0, 0, 0.4);
}

.brand {
  font-weight: 800;
  font-size: 1.85rem;
  letter-spacing: 0.06em;
  color: var(--accent);
  text-decoration: none;
}

.menu {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.auth-actions {
  display: inline-flex;
  align-items: center;
  gap: 10px;
}

.menu a,
.menu button {
  border: 1px solid transparent;
  border-radius: 12px;
  background: transparent;
  color: var(--text);
  text-decoration: none;
  font-size: 1rem;
  font-weight: 600;
  padding: 10px 15px;
  cursor: pointer;
  transition: all 0.22s ease;
}

.menu a:hover,
.menu button:hover {
  border-color: var(--line);
  background: rgba(91, 162, 255, 0.12);
  color: #fff;
}

.menu a.active {
  border-color: rgba(91, 162, 255, 0.42);
  background: rgba(56, 138, 255, 0.23);
  color: #fff;
}

.divider {
  width: 1px;
  height: 24px;
  background: var(--line);
  margin: 0 3px;
}

.icon-btn {
  width: 42px;
  height: 42px;
  border: 1px solid var(--line);
  border-radius: 12px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
  padding: 0;
}

#settings-btn i {
  pointer-events: none;
}

.btn-outline,
.btn-primary {
  padding: 10px 16px;
  border-radius: 12px;
  border: 1px solid var(--line);
}

.btn-outline {
  background: rgba(78, 163, 255, 0.08);
  color: var(--text);
}

.btn-primary {
  background: linear-gradient(135deg, var(--primary), var(--primary-strong));
  color: #fff;
  border-color: transparent;
  box-shadow: 0 8px 22px rgba(47, 134, 245, 0.34);
}

.hero {
  margin-top: 58px;
  display: grid;
  grid-template-columns: minmax(280px, 1fr) minmax(280px, 0.9fr);
  gap: 28px;
  align-items: stretch;
}

.hero-main,
.hero-side,
.notebook-main {
  border: 1px solid var(--line);
  border-radius: 24px;
  background: var(--card);
  backdrop-filter: blur(10px);
  box-shadow: 0 18px 34px rgba(2, 10, 25, 0.5);
}

.hero-main {
  padding: 34px;
}

.hero-main h1 {
  font-size: clamp(1.9rem, 3.2vw, 3rem);
  line-height: 1.15;
  margin-bottom: 16px;
}

.hero-main .sub {
  color: #c7dcfa;
  font-size: 1.1rem;
  margin-bottom: 28px;
}

.feature {
  margin-top: 18px;
  padding: 18px;
  border-radius: 16px;
  border: 1px solid var(--line);
  background: var(--hero-panel-bg);
}

.feature h2 {
  font-size: 1.1rem;
  margin-bottom: 8px;
  color: var(--accent);
}

.feature p {
  color: var(--text-soft);
  font-size: 0.98rem;
}

.hero-side {
  padding: 26px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 18px;
}

.stat {
  border-radius: 16px;
  border: 1px solid var(--line);
  padding: 16px 18px;
  background: var(--hero-panel-bg);
}

.stat strong {
  display: block;
  font-size: 1.8rem;
  color: var(--accent);
  margin-bottom: 3px;
}

.stat span {
  color: var(--text-soft);
  font-size: 0.95rem;
}

.notebook-main {
  margin-top: 58px;
  padding: 34px;
}

.notebook-main h1 {
  font-size: clamp(1.8rem, 3vw, 2.6rem);
  margin-bottom: 10px;
}

.notebook-main p {
  color: var(--text-soft);
}

.hidden {
  display: none !important;
}

.auth-modal {
  position: fixed;
  inset: 0;
  z-index: 50;
  background: var(--overlay-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 18px;
}

.auth-modal-card {
  width: min(420px, 100%);
  border-radius: 18px;
  border: 1px solid var(--line);
  background: var(--modal-bg);
  box-shadow: 0 24px 48px rgba(0, 0, 0, 0.42);
  padding: 18px;
}

.settings-modal-card {
  width: min(380px, 100%);
}

.settings-body {
  margin-top: 8px;
}

.settings-label {
  margin-bottom: 10px;
  color: var(--text-soft);
  font-size: 0.92rem;
}

.theme-segmented {
  display: inline-flex;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 12px;
  overflow: hidden;
  background: var(--surface-soft);
}

.theme-option {
  flex: 1;
  border: none;
  border-right: 1px solid var(--line);
  background: transparent;
  color: var(--text);
  padding: 10px 8px;
  font-weight: 700;
  cursor: pointer;
}

.theme-option:last-child {
  border-right: none;
}

.theme-option.active {
  background: linear-gradient(135deg, var(--primary), var(--primary-strong));
  color: #fff;
}

.auth-modal-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 14px;
}

.auth-modal-head h3 {
  font-size: 1.2rem;
}

.auth-form {
  display: grid;
  gap: 8px;
}

.auth-form label {
  font-size: 0.95rem;
  color: var(--text-soft);
}

.auth-form input {
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--input-bg);
  color: var(--text);
  padding: 10px 12px;
  outline: none;
}

.auth-form input:focus {
  border-color: rgba(110, 200, 255, 0.7);
}

.auth-submit {
  width: 100%;
  margin-top: 8px;
}

.auth-switch {
  margin-top: 10px;
  border: none;
  background: transparent;
  color: var(--accent);
  font-weight: 600;
  cursor: pointer;
}

.auth-status {
  min-height: 20px;
  font-size: 0.9rem;
  color: #ffb2b2;
}

.auth-status.success {
  color: #8df2b8;
}

@media (max-width: 860px) {
  body {
    padding: 14px;
  }

  .floating-nav {
    flex-direction: column;
    align-items: flex-start;
  }

  .menu {
    width: 100%;
  }

  .hero {
    margin-top: 30px;
    grid-template-columns: 1fr;
  }

  .hero-main,
  .hero-side,
  .notebook-main {
    padding: 22px;
  }
}

.notebook-layout {
  margin-top: 58px;
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 24px;
}

.notebook-left,
.notebook-right {
  border: 1px solid var(--line);
  border-radius: 20px;
  background: var(--card);
  padding: 18px;
}

.notebook-header-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.notebook-grid {
  margin-top: 16px;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
  gap: 12px;
}

.notebook-item-card {
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--surface-soft);
  color: var(--text);
  text-align: left;
  padding: 14px;
  cursor: pointer;
  transition: transform 0.15s ease, border-color 0.15s ease, background 0.15s ease;
}

.notebook-item-card:hover {
  transform: translateY(-3px);
  border-color: rgba(110, 200, 255, 0.45);
  background: var(--surface-hover);
}

.notebook-item-card.active {
  border-color: rgba(110, 200, 255, 0.7);
  background: linear-gradient(160deg, rgba(78, 163, 255, 0.28), var(--active-card-end));
}

.notebook-item-title {
  font-weight: 700;
}

.notebook-item-meta {
  margin-top: 6px;
  font-size: 0.92rem;
  color: var(--text-soft);
}

.notebook-detail {
  margin-top: 20px;
}

.notebook-detail-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.notebook-detail-head h2 {
  font-size: 1.25rem;
  margin-right: auto;
}

.notebook-detail-head #start-review-btn {
  white-space: nowrap;
}

.notebook-detail-head input {
  flex: 0 0 320px;
  max-width: 100%;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--line);
  background: var(--input-bg);
  color: var(--text);
}

/* vocab list */
.vocab-list {
  display: grid;
  gap: 14px;
  margin-top: 16px;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
}

.vocab-card {
  min-height: 190px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  padding: 18px;
  border-radius: 16px;
  border: 1px solid var(--card-border-soft);
  background: var(--surface-strong);
  color: var(--text);
  transition: transform .14s ease, background .14s ease;
}

.vocab-card:hover {
  transform: translateY(-4px);
  background: var(--surface-hover);
}

.vocab-card-main h3 {
  font-size: 1.95rem;
  line-height: 1.2;
}

.vocab-card-phonetic {
  margin-top: 10px;
  color: var(--text-soft);
  font-style: italic;
  font-size: 1.15rem;
}

.vocab-card-meaning {
  margin-top: 12px;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text);
}

.vocab-card-actions {
  margin-top: 14px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.vocab-card-level {
  font-size: 0.9rem;
  color: var(--muted-strong);
}

.vocab-card-buttons {
  display: flex;
  gap: 8px;
}

.vocab-card .btn-outline {
  color: var(--text);
  border-color: var(--card-border-strong);
  background: var(--surface-elevated);
}

.vocab-card .audio-btn {
  color: var(--text);
  border: 1px solid var(--card-border-strong);
  border-radius: 12px;
  padding: 8px 10px;
  background: var(--surface-elevated);
  cursor: pointer;
}

.empty-state {
  padding: 16px;
  border: 1px dashed var(--line);
  border-radius: 12px;
  color: var(--text-soft);
}

.sr-card h2 { margin-bottom: 6px; color: var(--accent); }
.sr-item {
  display: flex;
  justify-content: space-between;
  padding: 10px;
  border-radius: 12px;
  background: var(--surface-soft);
  margin-bottom: 8px;
  cursor: pointer;
  border: 1px solid transparent;
  transition: background .14s ease, border-color .14s ease, transform .14s ease;
}

.sr-item:hover {
  background: var(--surface-hover);
  border-color: var(--card-border-strong);
  transform: translateY(-1px);
}

@media (max-width: 960px) {
  .notebook-layout {
    grid-template-columns: 1fr;
  }

  .notebook-detail-head {
    flex-direction: column;
    align-items: flex-start;
  }

  .notebook-detail-head input {
    width: 100%;
    flex-basis: auto;
  }
}