:root {
  color-scheme: light dark;
  --bg: #f8f8fb;
  --fg: #1c2333;
  --accent: #3f6de0;
  --accent-soft: rgba(63, 109, 224, 0.14);
  --danger: #d64545;
  --success: #2f9d5d;
  --card-bg: #ffffff;
  --card-shadow: 0 18px 35px -20px rgba(16, 33, 58, 0.6);
  --radius-lg: 18px;
  font-family: "Inter", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--fg);
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: 32px 16px 64px;
}

.app {
  width: min(960px, 100%);
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.app__header {
  text-align: center;
  padding: 12px 8px 0;
}

.app__header h1 {
  margin: 0 0 8px;
  font-size: clamp(1.6rem, 2vw + 1rem, 2.4rem);
}

.app__header p {
  margin: 0;
  color: rgba(28, 35, 51, 0.75);
}

.app__controls {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  justify-content: center;
}

.control-button {
  appearance: none;
  border: none;
  border-radius: 999px;
  padding: 12px 22px;
  background: var(--accent);
  color: white;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s, background 0.2s;
  box-shadow: var(--card-shadow);
}

.control-button:hover,
.control-button:focus-visible {
  transform: translateY(-1px);
  box-shadow: 0 18px 38px -21px rgba(28, 35, 51, 0.55);
}

.control-button.secondary {
  background: var(--accent-soft);
  color: var(--accent);
  box-shadow: none;
}

.mode-section {
  background: var(--card-bg);
  border-radius: var(--radius-lg);
  padding: 24px;
  box-shadow: var(--card-shadow);
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.hidden {
  display: none !important;
}

.status-bar {
  display: flex;
  justify-content: space-between;
  font-weight: 600;
  color: rgba(28, 35, 51, 0.7);
}

.card-area {
  display: flex;
  justify-content: center;
  perspective: 1200px;
}

.card {
  width: min(420px, 90%);
  height: 260px;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.6s cubic-bezier(0.2, 0.8, 0.2, 1);
  cursor: pointer;
}

.card.flipped {
  transform: rotateY(180deg);
}

.card--disabled {
  cursor: default;
  opacity: 0.6;
  pointer-events: none;
}

.card__face {
  position: absolute;
  inset: 0;
  border-radius: var(--radius-lg);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 24px;
  gap: 16px;
  background: linear-gradient(145deg, #ffffff, #f1f3ff);
  backface-visibility: hidden;
  box-shadow: var(--card-shadow);
}

.card__face--back {
  transform: rotateY(180deg);
}

.card__face p {
  margin: 0;
  text-align: center;
  font-size: clamp(1.4rem, 1.2vw + 1.2rem, 2rem);
  line-height: 1.3;
}

.card__language {
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  font-weight: 700;
  text-transform: uppercase;
  color: rgba(28, 35, 51, 0.5);
}

.hint {
  text-align: center;
  color: rgba(28, 35, 51, 0.65);
  font-size: 0.95rem;
}

.actions {
  display: flex;
  gap: 16px;
  justify-content: center;
}

.action-button {
  min-width: 140px;
  padding: 16px 22px;
  border-radius: 14px;
  border: none;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
  box-shadow: var(--card-shadow);
}

.action-button--unknown {
  background: var(--danger);
  color: white;
}

.action-button--known {
  background: var(--success);
  color: white;
}

.action-button:active {
  transform: scale(0.98);
}

.exam-status {
  display: flex;
  justify-content: space-between;
  font-weight: 600;
  color: rgba(28, 35, 51, 0.7);
}

.exam-question {
  text-align: center;
}

.exam-question h2 {
  margin: 0 0 8px;
}

.exam-question p {
  margin: 0;
  font-size: clamp(1.3rem, 1vw + 1.2rem, 1.8rem);
  font-weight: 600;
}

.exam-options {
  display: grid;
  gap: 12px;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
}

.exam-option {
  border: none;
  border-radius: 16px;
  padding: 18px 20px;
  background: rgba(63, 109, 224, 0.08);
  color: var(--fg);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s, transform 0.2s;
}

.exam-option:hover,
.exam-option:focus-visible {
  background: rgba(63, 109, 224, 0.16);
  transform: translateY(-2px);
}

.exam-option.correct {
  background: rgba(47, 157, 93, 0.18);
  color: var(--success);
}

.exam-option.incorrect {
  background: rgba(214, 69, 69, 0.16);
  color: var(--danger);
}

.exam-feedback {
  text-align: center;
  font-weight: 600;
  min-height: 1.4em;
}

.exam-next {
  align-self: center;
}

@media (max-width: 640px) {
  body {
    padding: 24px 12px 48px;
  }

  .mode-section {
    padding: 18px;
  }

  .card {
    height: 220px;
  }

  .actions {
    flex-direction: column;
  }

  .action-button {
    width: 100%;
  }

  .app__controls {
    gap: 8px;
  }

  .control-button {
    flex: 1 1 45%;
    font-size: 0.9rem;
    padding: 10px 16px;
  }
}