Flashcard Learning App

<div class="flashcard-container">
  <div class="deck-header">
    <span id="card-progress">Card 1 of 4</span>
    <button id="shuffle-deck-btn" class="icon-tool-btn" title="Shuffle Deck"><i class="fas fa-random"></i></button>
  </div>

  <div class="flashcard-scene" id="card-scene">
    <div class="flashcard" id="active-card">
      <div class="card-side card-front">
        <span class="card-tag">Question</span>
        <h3 id="card-question">What is closure in JavaScript?</h3>
        <span class="flip-hint"><i class="fas fa-sync-alt"></i> Click to flip</span>
      </div>
      <div class="card-side card-back">
        <span class="card-tag">Answer</span>
        <p id="card-answer">A closure is a function bundled with references to its surrounding lexical environment.</p>
        <span class="flip-hint"><i class="fas fa-sync-alt"></i> Click to flip</span>
      </div>
    </div>
  </div>

  <div class="nav-controls">
    <button id="btn-prev-card" class="btn-nav"><i class="fas fa-arrow-left"></i> Prev</button>
    <button id="btn-flip-card" class="btn-flip"><i class="fas fa-undo"></i> Flip</button>
    <button id="btn-next-card" class="btn-nav">Next <i class="fas fa-arrow-right"></i></button>
  </div>
</div>

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
}
body {
  background: #0f172a;
  color: #f8fafc;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
}
.flashcard-container {
  background: #1e293b;
  border: 1px solid #334155;
  border-radius: 24px;
  padding: 28px;
  width: 100%;
  max-width: 440px;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4);
}
.deck-header {
  display: flex;
  justify-content: space-between;
  color: #94a3b8;
  font-size: 0.85rem;
  font-weight: 600;
  margin-bottom: 20px;
}
.icon-tool-btn {
  background: none;
  border: none;
  color: #38bdf8;
  cursor: pointer;
  font-size: 1rem;
}
.flashcard-scene {
  perspective: 1000px;
  height: 220px;
  margin-bottom: 24px;
}
.flashcard {
  width: 100%;
  height: 100%;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  cursor: pointer;
}
.flashcard.flipped { transform: rotateY(180deg); }
.card-side {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: 16px;
  padding: 24px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  border: 1px solid #334155;
}
.card-front { background: #0f172a; color: #f8fafc; }
.card-back { background: #0c4a6e; border-color: #0284c7; transform: rotateY(180deg); }
.card-tag { font-size: 0.75rem; text-transform: uppercase; font-weight: 700; color: #38bdf8; }
.card-front h3 { font-size: 1.25rem; line-height: 1.4; }
.card-back p { font-size: 1rem; line-height: 1.5; color: #e0f2fe; }
.flip-hint { font-size: 0.75rem; color: #64748b; }
.nav-controls { display: flex; gap: 10px; }
.btn-nav, .btn-flip { flex: 1; padding: 12px 0; border: none; border-radius: 10px; font-weight: 700; cursor: pointer; }
.btn-nav { background: #334155; color: #f8fafc; }
.btn-flip { background: #38bdf8; color: #0f172a; }

const deck = [
  { q: 'What is a Closure in JavaScript?', a: 'A function bundled together with references to its surrounding lexical environment.' },
  { q: 'What is the Event Loop?', a: 'The runtime mechanism that coordinates the execution of code, collecting events, and queued sub-tasks.' },
  { q: 'What is the difference between == and ===?', a: '== checks value equality with type coercion; === checks strict value and type equality.' },
  { q: 'What is a Promise in JS?', a: 'An object representing the eventual completion (or failure) of an asynchronous operation.' }
];

let currentIndex = 0;
const card = document.getElementById('active-card');
const qEl = document.getElementById('card-question');
const aEl = document.getElementById('card-answer');
const progressEl = document.getElementById('card-progress');
const btnPrev = document.getElementById('btn-prev-card');
const btnNext = document.getElementById('btn-next-card');
const btnFlip = document.getElementById('btn-flip-card');
const shuffleBtn = document.getElementById('shuffle-deck-btn');

function updateCard() {
  card.classList.remove('flipped');
  setTimeout(() => {
    qEl.textContent = deck[currentIndex].q;
    aEl.textContent = deck[currentIndex].a;
    progressEl.textContent = `Card ${currentIndex + 1} of ${deck.length}`;
  }, 150);
}

card.addEventListener('click', () => card.classList.toggle('flipped'));
btnFlip.addEventListener('click', () => card.classList.toggle('flipped'));

btnNext.addEventListener('click', () => {
  currentIndex = (currentIndex + 1) % deck.length;
  updateCard();
});

btnPrev.addEventListener('click', () => {
  currentIndex = (currentIndex - 1 + deck.length) % deck.length;
  updateCard();
});

shuffleBtn.addEventListener('click', () => {
  deck.sort(() => Math.random() - 0.5);
  currentIndex = 0;
  updateCard();
});

updateCard();