:root {
  --bg-1: #081122;
  --bg-2: #0f1c35;
  --bg-3: #14284d;
  --surface-1: #18253d;
  --surface-2: #22324f;
  --surface-3: #2a3954;
  --border-1: rgba(255, 255, 255, 0.12);
  --border-2: rgba(255, 255, 255, 0.08);
  --text: #f8fafc;
  --muted: #cbd5e1;
  --accent: #38bdf8;
  --accent-2: #0ea5e9;
  --shadow-lg: 0 24px 70px rgba(0, 0, 0, 0.42);
  --shadow-md: 0 14px 30px rgba(0, 0, 0, 0.3);
  --radius-xl: 24px;
  --radius-lg: 18px;
  --radius-md: 14px;
  --slide-duration: 280ms;
  --flip-duration: 700ms;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
}

body {
  font-family: Arial, Helvetica, sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at top, rgba(37, 99, 235, 0.35) 0%, transparent 24%),
    linear-gradient(160deg, var(--bg-1), var(--bg-2) 55%, var(--bg-3));
  min-height: 100vh;
  padding: 24px;
}

button,
input,
textarea,
select {
  font: inherit;
}

button {
  -webkit-tap-highlight-color: transparent;
}

.app {
  width: 100%;
  max-width: 980px;
  margin: 0 auto;
}

.topbar {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 24px;
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-size: 0.82rem;
  font-weight: 800;
}

h1 {
  margin: 0;
  font-size: clamp(2rem, 4vw, 3rem);
}

.counter-wrap {
  display: flex;
  align-items: center;
  justify-content: center;
}

.counter {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 98px;
  padding: 12px 18px;
  border-radius: 999px;
  background: var(--surface-3);
  border: 1px solid var(--border-1);
  color: var(--text);
  font-weight: 800;
  box-shadow: var(--shadow-md);
}

.viewer {
  display: grid;
  gap: 20px;
}

.flashcard-scene {
  width: 100%;
  perspective: 1200px;
}

.flashcard-slider {
  width: 100%;
  transition:
    transform var(--slide-duration) ease,
    opacity var(--slide-duration) ease;
  will-change: transform, opacity;
}

.flashcard-slider.is-sliding-out-left {
  transform: translateX(-72px);
  opacity: 0;
}

.flashcard-slider.is-sliding-out-right {
  transform: translateX(72px);
  opacity: 0;
}

.flashcard-slider.is-pre-enter-left {
  transform: translateX(-72px);
  opacity: 0;
}

.flashcard-slider.is-pre-enter-right {
  transform: translateX(72px);
  opacity: 0;
}

.flashcard-slider.is-entering {
  transform: translateX(0);
  opacity: 1;
}

.flashcard {
  position: relative;
  width: 100%;
  min-height: 460px;
  cursor: pointer;
  outline: none;
  transform-style: preserve-3d;
  transition: transform var(--flip-duration) ease;
}

.flashcard:focus-visible {
  box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.45);
  border-radius: var(--radius-xl);
}

.flashcard.is-flipped {
  transform: rotateY(180deg);
}

.flashcard-face {
  position: absolute;
  inset: 0;
  display: flex;
  min-height: 460px;
  width: 100%;
  flex-direction: column;
  gap: 18px;
  padding: 24px;
  border-radius: var(--radius-xl);
  border: 1px solid var(--border-1);
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.02), rgba(255, 255, 255, 0.01)),
    linear-gradient(160deg, #24324c, #2c3b58 60%, #243550);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

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

.flashcard-front::before,
.flashcard-back::before {
  content: "";
  position: absolute;
  right: -70px;
  bottom: -70px;
  width: 210px;
  height: 210px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(56, 189, 248, 0.12), transparent 70%);
  pointer-events: none;
}

.flashcard-front::after,
.flashcard-back::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(120deg, rgba(255, 255, 255, 0.03), transparent 30%);
  pointer-events: none;
}

.face-label {
  margin: 0;
  color: var(--accent);
  font-size: 0.86rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-weight: 800;
}

.flashcard.is-flipped .flashcard-face {
  background:
    linear-gradient(180deg, rgba(56, 189, 248, 0.08), rgba(14, 165, 233, 0.05)),
    linear-gradient(160deg, #1f2e4a, #2b3d5e 60%, #223552);
}

.flashcard.is-flipped .face-label {
  color: #22c55e;
}

.card-content {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  font-size: clamp(1.2rem, 2.4vw, 1.75rem);
  line-height: 1.55;
  font-weight: 800;
  padding: 12px;
  word-break: break-word;
}

.card-content br {
  display: block;
  content: "";
  margin-bottom: 10px;
}

.actions,
.nav {
  display: flex;
  gap: 14px;
}

.actions {
  justify-content: center;
}

.nav {
  justify-content: space-between;
}

.btn {
  appearance: none;
  border: 1px solid var(--border-1);
  border-radius: var(--radius-md);
  padding: 14px 18px;
  cursor: pointer;
  font-weight: 800;
  box-shadow: var(--shadow-md);
  transition:
    transform 150ms ease,
    opacity 150ms ease;
}

.btn:disabled {
  cursor: not-allowed;
  opacity: 0.55;
}

.btn-primary {
  min-width: 210px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #00111a;
  border-color: rgba(255, 255, 255, 0.4);
}

.btn-secondary {
  flex: 1;
  background: var(--surface-3);
  color: var(--text);
}

.hint {
  margin: 0;
  text-align: center;
  color: var(--muted);
  font-size: 0.95rem;
  line-height: 1.5;
}

/* Container do botão de aleatorizar (linha separada, centralizado) */
.shuffle-wrap {
  display: flex;
  justify-content: center;
  margin-top: 8px;
}

/* Botão terciário (menos destaque que os outros) */
.btn-tertiary {
  appearance: none;
  border-radius: var(--radius-md);
  padding: 10px 16px;
  cursor: pointer;
  font-weight: 700;

  /* visual mais leve */
  background: transparent;
  color: var(--muted);
  border: 1px solid var(--border-2);

  /* menor largura */
  min-width: 160px;

  /* transição suave */
  transition:
    background 150ms ease,
    color 150ms ease,
    border-color 150ms ease,
    transform 120ms ease;
}

.btn-tertiary:hover {
  background: rgba(255, 255, 255, 0.04);
  color: var(--text);
  border-color: var(--border-1);
}

.btn-tertiary:active {
  transform: scale(0.98);
}

.btn-tertiary:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

@media (max-width: 768px) {
  body {
    padding: 16px;
  }

  .topbar {
    flex-direction: column;
    align-items: stretch;
  }

  .counter-wrap {
    justify-content: flex-start;
  }

  .flashcard {
    min-height: 420px;
  }

  .flashcard-face {
    min-height: 420px;
    padding: 20px;
  }

  .card-content {
    font-size: clamp(1.05rem, 4.8vw, 1.35rem);
  }

  .nav {
    flex-direction: row;
  }

  .btn-secondary,
  .btn-primary {
    width: 100%;
  }

  .hint {
    font-size: 0.88rem;
  }

  .flashcard-slider.is-sliding-out-left {
    transform: translateX(-48px);
  }

  .flashcard-slider.is-sliding-out-right {
    transform: translateX(48px);
  }

  .flashcard-slider.is-pre-enter-left {
    transform: translateX(-48px);
  }

  .flashcard-slider.is-pre-enter-right {
    transform: translateX(48px);
  }
}

@media (max-width: 420px) {
  .flashcard {
    min-height: 380px;
  }

  .flashcard-face {
    min-height: 380px;
    padding: 16px;
    border-radius: 20px;
  }

  .card-content {
    padding: 4px;
    line-height: 1.45;
  }
}