:root {
  --viet-bg: #f7f7f5;
  --viet-surface: #ffffff;
  --viet-ink: #1a1a1a;
  --viet-muted: #6b6b6b;
  --viet-line: #e3e3df;
  --viet-accent: #2d6a4f;
  --viet-accent-soft: #d8f3dc;
  --viet-north: #1d4e89;
  --viet-south: #bc4749;
  --viet-common: #6b6b6b;
  --viet-radius: 12px;
  --viet-shadow: 0 1px 3px rgba(0, 0, 0, 0.06), 0 8px 24px rgba(0, 0, 0, 0.04);
  --viet-mono: "IBM Plex Mono", "Consolas", monospace;
  --viet-sans: "IBM Plex Sans JP", "Hiragino Sans", sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: var(--viet-sans);
  color: var(--viet-ink);
  background: var(--viet-bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

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

.viet-container {
  width: min(920px, 92%);
  margin: 0 auto;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

.viet-muted { color: var(--viet-muted); font-size: 0.92rem; }

/* Header */
.viet-header {
  background: var(--viet-surface);
  border-bottom: 1px solid var(--viet-line);
  position: sticky;
  top: 0;
  z-index: 20;
}

.viet-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 56px;
  gap: 1rem;
}

.viet-logo {
  display: flex;
  flex-direction: column;
  line-height: 1.25;
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--viet-ink);
  text-decoration: none;
}

.viet-logo__tag {
  font-size: 0.72rem;
  font-weight: 500;
  color: var(--viet-muted);
}

.viet-nav {
  display: flex;
  gap: 0.75rem;
  align-items: center;
  font-size: 0.92rem;
}

.viet-nav a { color: var(--viet-muted); text-decoration: none; }
.viet-nav a:hover { color: var(--viet-ink); }
.viet-nav__active {
  color: var(--viet-accent) !important;
  font-weight: 500;
}
.viet-nav__cta {
  color: var(--viet-accent) !important;
  font-weight: 500;
}

.viet-main { padding: 2rem 0 4rem; min-height: 60vh; }

/* Hero */
.viet-hero {
  padding: 2.5rem 0 1.5rem;
}

.viet-eyebrow {
  font-size: 0.85rem;
  color: var(--viet-muted);
  margin: 0 0 0.5rem;
  letter-spacing: 0.04em;
}

.viet-hero__title {
  font-size: clamp(1.75rem, 4vw, 2.35rem);
  font-weight: 600;
  line-height: 1.25;
  margin: 0 0 1rem;
}

.viet-asof {
  display: block;
  margin-top: 0.35rem;
  font-size: 0.42em;
  font-weight: 400;
  color: var(--viet-muted);
  letter-spacing: 0.02em;
}

.viet-hero__lead {
  color: var(--viet-muted);
  max-width: 36em;
  margin: 0 0 1.5rem;
}

.viet-hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

/* Buttons */
.viet-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.55rem 1.1rem;
  border-radius: 8px;
  border: 1px solid transparent;
  font: inherit;
  font-size: 0.92rem;
  cursor: pointer;
  text-decoration: none;
  transition: background 0.15s, border-color 0.15s;
}

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

.viet-btn--primary:hover {
  background: #24573f;
  text-decoration: none;
  color: #fff;
}

.viet-btn--ghost {
  background: var(--viet-surface);
  border-color: var(--viet-line);
  color: var(--viet-ink);
}

.viet-btn--ghost:hover:not(:disabled) {
  border-color: #ccc;
  text-decoration: none;
}

.viet-btn--sm { padding: 0.35rem 0.75rem; font-size: 0.85rem; }
.viet-btn:disabled { opacity: 0.45; cursor: not-allowed; }

/* Stats */
.viet-stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0 2.5rem;
}

.viet-stat {
  background: var(--viet-surface);
  border: 1px solid var(--viet-line);
  border-radius: var(--viet-radius);
  padding: 1rem;
  text-align: center;
}

.viet-stat__num {
  display: block;
  font-size: 1.6rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.viet-stat__label {
  font-size: 0.82rem;
  color: var(--viet-muted);
}

.viet-section__title {
  font-size: 1.1rem;
  margin: 0 0 0.75rem;
}

.viet-feature-list {
  margin: 0;
  padding-left: 1.2rem;
  color: var(--viet-muted);
}

/* Filters */
.viet-page-head h1 {
  margin: 0 0 0.25rem;
  font-size: 1.5rem;
}

.viet-filters {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 1.25rem 0 1.5rem;
}

.viet-input,
.viet-select {
  font: inherit;
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--viet-line);
  border-radius: 8px;
  background: var(--viet-surface);
}

.viet-input { flex: 1 1 200px; min-width: 0; }

/* Word list */
.viet-word-list {
  list-style: none;
  margin: 0;
  padding: 0;
  border: 1px solid var(--viet-line);
  border-radius: var(--viet-radius);
  background: var(--viet-surface);
  overflow: hidden;
}

.viet-word-item {
  display: grid;
  grid-template-columns: auto 1fr;
  grid-template-rows: auto auto;
  gap: 0.15rem 0.75rem;
  padding: 0.85rem 1rem;
  border-bottom: 1px solid var(--viet-line);
  text-decoration: none;
  color: inherit;
}

.viet-word-item:last-child { border-bottom: none; }
.viet-word-item:hover { background: #fafaf8; text-decoration: none; }

.viet-word-item__vi {
  grid-column: 2;
  font-family: var(--viet-mono);
  font-size: 0.95rem;
}

.viet-word-item__ja {
  grid-column: 2;
  font-size: 0.85rem;
  color: var(--viet-muted);
}

.viet-pill {
  grid-row: 1 / 3;
  align-self: start;
  font-size: 0.72rem;
  font-weight: 500;
  padding: 0.15rem 0.45rem;
  border-radius: 999px;
  border: 1px solid var(--viet-line);
  color: var(--viet-muted);
  white-space: nowrap;
}

.viet-pill--north { color: var(--viet-north); border-color: #b8cfe8; background: #eef4fb; }
.viet-pill--south { color: var(--viet-south); border-color: #e8b8b8; background: #fdf0f0; }
.viet-pill--common { color: var(--viet-common); }

.viet-pagination {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  margin-top: 1.5rem;
}

.viet-empty {
  text-align: center;
  color: var(--viet-muted);
  padding: 3rem 1rem;
}

/* Flashcard */
.flashcard {
  perspective: 1200px;
  max-width: 480px;
  margin: 0 auto;
}

.flashcard__inner {
  position: relative;
  min-height: 280px;
  transition: transform 0.45s cubic-bezier(0.4, 0.2, 0.2, 1);
  transform-style: preserve-3d;
}

.flashcard--instant .flashcard__inner {
  transition: none !important;
}

.flashcard--swapping {
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.16s ease;
}

.flashcard--swapping .flashcard__inner {
  transition: none !important;
}

.flashcard[data-flipped="true"] .flashcard__inner {
  transform: rotateY(180deg);
}

.flashcard__face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  background: var(--viet-surface);
  border: 1px solid var(--viet-line);
  border-radius: var(--viet-radius);
  box-shadow: var(--viet-shadow);
  padding: 1.75rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.flashcard__back {
  transform: rotateY(180deg);
}

.flashcard__label {
  margin: 0;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--viet-muted);
}

.flashcard__vi {
  margin: 0;
  font-family: var(--viet-mono);
  font-size: 1.35rem;
  line-height: 1.45;
  white-space: pre-wrap;
}

.flashcard__ja {
  margin: 0;
  font-size: 1.15rem;
  white-space: pre-wrap;
}

.flashcard__hint,
.flashcard__note {
  margin: 0.5rem 0 0;
  font-size: 0.88rem;
  color: var(--viet-muted);
  background: var(--viet-accent-soft);
  padding: 0.6rem 0.75rem;
  border-radius: 8px;
}

.flashcard__meta {
  margin: auto 0 0;
  font-size: 0.8rem;
  color: var(--viet-muted);
}

.flashcard__input-wrap { margin-top: auto; }

.flashcard__input {
  width: 100%;
  font-family: var(--viet-mono);
  font-size: 1rem;
  padding: 0.65rem 0.75rem;
  border: 1px solid var(--viet-line);
  border-radius: 8px;
  background: var(--viet-bg);
}

.flashcard__input:focus {
  outline: 2px solid var(--viet-accent-soft);
  border-color: var(--viet-accent);
}

.viet-card-page,
.viet-study {
  max-width: 520px;
}

.viet-breadcrumb { margin-bottom: 1rem; font-size: 0.9rem; }

.viet-card-actions {
  display: flex;
  justify-content: center;
  gap: 0.75rem;
  margin: 1.25rem 0;
}

.viet-card-nav {
  display: flex;
  justify-content: space-between;
  gap: 0.5rem;
}

/* Study preview */
.viet-study__head { margin-bottom: 1.25rem; }
.viet-study__head h1 { margin: 0 0 0.35rem; font-size: 1.25rem; }

.viet-progress {
  height: 4px;
  background: var(--viet-line);
  border-radius: 999px;
  overflow: hidden;
  margin: 1rem 0 0.35rem;
}

.viet-progress__bar {
  height: 100%;
  background: var(--viet-accent);
  border-radius: 999px;
}

.viet-progress__label {
  margin: 0;
  font-size: 0.82rem;
  color: var(--viet-muted);
}

.viet-rating {
  margin-top: 1.5rem;
  text-align: center;
}

.viet-rating__label {
  margin: 0 0 0.75rem;
  font-size: 0.88rem;
  color: var(--viet-muted);
}

.viet-rating__buttons {
  display: flex;
  justify-content: center;
  gap: 0.65rem;
}

.viet-rate {
  width: 3rem;
  height: 3rem;
  border-radius: 50%;
  border: 1px solid var(--viet-line);
  background: var(--viet-surface);
  font-size: 1.2rem;
  cursor: pointer;
  transition: transform 0.12s, border-color 0.12s;
}

.viet-rate:hover { transform: scale(1.06); border-color: #bbb; }
.viet-rate--best:hover { border-color: var(--viet-accent); color: var(--viet-accent); }

.viet-rating__legend {
  margin: 0.75rem 0 0;
  font-size: 0.78rem;
  color: var(--viet-muted);
}

/* Footer */
.viet-footer {
  border-top: 1px solid var(--viet-line);
  padding: 1.5rem 0 2rem;
  font-size: 0.82rem;
  color: var(--viet-muted);
}

.viet-footer__note { margin: 0 0 0.35rem; }

.viet-footer__teacher {
  font-weight: 600;
  color: var(--viet-accent);
}

.viet-youtube-link {
  font-weight: 500;
  white-space: nowrap;
}

.viet-sponsors {
  margin-top: 1rem;
}

.viet-sponsors__label {
  margin: 0 0 0.5rem;
  font-size: 0.82rem;
  color: var(--viet-muted);
  font-weight: 500;
}

.viet-sponsors__plates {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  align-items: stretch;
}

.viet-sponsor {
  display: inline-flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0.5rem 0.85rem;
  border: 1px solid var(--viet-line);
  border-radius: 8px;
  background: var(--viet-surface);
  text-decoration: none;
  color: var(--viet-muted);
  font-size: 0.82rem;
  min-height: 52px;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
}

.viet-sponsor:hover {
  border-color: #ddb8c4;
  text-decoration: none;
  color: var(--viet-ink);
}

.viet-sponsor img,
.viet-sponsor__img {
  display: block;
  height: 40px;
  width: auto;
  object-fit: contain;
}

.viet-sponsor__img--round {
  height: 44px;
  width: 44px;
  border-radius: 50%;
}

.viet-sponsor__icon--kotonoha {
  display: inline-flex;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  overflow: hidden;
  flex-shrink: 0;
  background: #f7f5f0;
}

.viet-sponsor__icon--kotonoha img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

/* Study guide */
.viet-guide {
  background: var(--viet-surface);
  border: 1px solid var(--viet-line);
  border-left: 3px solid var(--viet-accent);
  border-radius: var(--viet-radius);
  padding: 1rem 1.1rem;
  margin-bottom: 1.25rem;
}

.viet-guide__head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 0.5rem;
}

.viet-guide__close {
  border: none;
  background: transparent;
  font-size: 1.25rem;
  line-height: 1;
  cursor: pointer;
  color: var(--viet-muted);
  padding: 0.15rem 0.35rem;
}

.viet-guide__steps {
  margin: 0;
  padding-left: 0;
  list-style: none;
  font-size: 0.92rem;
  color: var(--viet-muted);
}

.viet-guide__steps li {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 0.35rem;
}

.viet-guide__steps span {
  flex-shrink: 0;
  width: 1.25rem;
  height: 1.25rem;
  border-radius: 50%;
  background: var(--viet-accent-soft);
  color: var(--viet-accent);
  font-size: 0.75rem;
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.viet-guide__note {
  margin: 0.5rem 0 0;
  font-size: 0.82rem;
  color: var(--viet-muted);
}

.viet-study__hint {
  text-align: center;
  margin: 1rem 0 0;
  font-size: 0.88rem;
}

.viet-feature-list--ordered {
  list-style: decimal;
  padding-left: 1.25rem;
}

.viet-study-done h1 {
  margin: 0 0 0.35rem;
}

.viet-lead {
  color: var(--viet-muted);
  margin: 0 0 1.5rem;
}

.flashcard--transition {
  opacity: 0.55;
  transform: scale(0.98);
  transition: opacity 0.16s ease, transform 0.16s ease;
}

@media (max-width: 520px) {
  .viet-main { padding-top: 1.25rem; }
  .flashcard__face { padding: 1.25rem 1rem; }
  .flashcard__vi { font-size: 1.15rem; }
}