:root {
  --surface: #ffffff;
  --ink: #111111;
  --muted: #5f5f5f;
  --accent: #2563eb;
  --accent-soft: #e0e7ff;
  --border: #e5e7eb;
  --success: #16a34a;
  --hidden: #111111;
  --page-bg: #f5f6fa;
  --panel-shadow: 0 10px 30px rgba(15, 23, 42, 0.05);
  --control-bg: #f8fafc;
  --toggle-ghost: transparent;
  --hidden-bg: #111111;
}

body.theme-dark {
  --surface: #15171c;
  --ink: #f3f4f6;
  --muted: #c7c9d1;
  --accent: #7aa2ff;
  --accent-soft: rgba(122, 162, 255, 0.18);
  --border: #2a2f3a;
  --success: #4ade80;
  --hidden: #0b0d12;
  --page-bg: #0f1116;
  --panel-shadow: 0 10px 30px rgba(0, 0, 0, 0.4);
  --control-bg: #1c2029;
  --toggle-ghost: rgba(255, 255, 255, 0.08);
  --hidden-bg: #0b0d12;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Inter", "Segoe UI", sans-serif;
  background: var(--page-bg);
  color: var(--ink);
  min-height: 100vh;
}

.page-header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
}

.page-header__inner {
  max-width: 1000px;
  margin: 0 auto;
  padding: 24px 20px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.page-header h1 {
  margin: 0 0 8px;
  font-size: 1.8rem;
}

.page-header p {
  margin: 0;
  color: var(--muted);
}

.theme-toggle {
  align-self: flex-start;
  border: 1px solid var(--border);
  background: var(--control-bg);
  color: var(--ink);
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 0.9rem;
  cursor: pointer;
}

.theme-toggle:focus {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

.menu {
  max-width: 1000px;
  margin: 0 auto;
  padding: 28px 20px 24px;
  display: grid;
  gap: 24px;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
}

.menu.is-hidden {
  display: none;
}

.menu__panel {
  background: var(--surface);
  border-radius: 16px;
  border: 1px solid var(--border);
  padding: 20px;
  box-shadow: var(--panel-shadow);
}

.menu__title {
  margin: 0 0 16px;
  font-size: 1.2rem;
}

.menu__list {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.menu__button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 100%;
  border: 1px solid transparent;
  background: var(--accent-soft);
  color: var(--accent);
  padding: 16px;
  border-radius: 12px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.menu__button:hover {
  transform: translateY(-1px);
  box-shadow: 0 8px 16px rgba(37, 99, 235, 0.18);
}

.menu__button:focus {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

.menu__details {
  min-height: 220px;
  color: var(--muted);
}

.menu__empty {
  margin: 0;
}

.menu__error {
  margin: 0;
  color: #dc2626;
}

.details {
  color: var(--ink);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.details__title {
  margin: 0;
}

.details__meta {
  margin: 0;
}

.details__label {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-weight: 600;
  color: var(--ink);
}

.details__input {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 10px;
  font-size: 0.95rem;
  width: 140px;
}

.details__begin {
  border: none;
  background: var(--accent);
  color: #ffffff;
  padding: 10px 16px;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  align-self: flex-start;
}

.details__begin:focus {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

.exercise {
  max-width: 1000px;
  margin: 0 auto 40px;
  padding: 0 20px 40px;
  display: grid;
  gap: 24px;
  grid-template-columns: minmax(280px, 420px) 1fr;
}

.exercise.is-hidden {
  display: none;
}

.exercise__player {
  background: var(--surface);
  border-radius: 16px;
  border: 1px solid var(--border);
  padding: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 220px;
  position: sticky;
  top: 16px;
  align-self: start;
}

.exercise__player iframe {
  width: 100%;
  max-width: 400px;
}

.exercise__text {
  background: var(--surface);
  border-radius: 16px;
  border: 1px solid var(--border);
  padding: 20px;
  white-space: pre-wrap;
  overflow: auto;
  min-height: 220px;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.exercise__controls {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.toggle-button {
  border: 1px solid var(--border);
  background: var(--control-bg);
  color: var(--ink);
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 0.9rem;
  cursor: pointer;
}

.toggle-button--ghost {
  background: var(--toggle-ghost);
}

.toggle-button:focus {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

.exercise__content {
  line-height: 1.7;
}

.cloze-word {
  border: none;
  background: transparent;
  color: var(--ink);
  font: inherit;
  padding: 2px 6px;
  margin: 0 2px;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.2s ease;
}

.cloze-word.is-hidden {
  background: var(--hidden-bg);
  color: var(--hidden-bg);
}

.cloze-word:focus {
  outline: 2px solid rgba(37, 99, 235, 0.5);
  outline-offset: 2px;
}

@media (max-width: 900px) {
  .exercise {
    grid-template-columns: 1fr;
  }
}