:root {
  --bg: #0f172a;
  --card: rgba(255,255,255,0.05);
  --accent: #3b82f6;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --flash: rgba(59,130,246,0.2);
  --correct: #00ff00;
  --skipped: #facc15;
}
* { box-sizing: border-box; }
body {
  margin:0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: linear-gradient(135deg, #0f172a, #1e293b);
  color: var(--text);
  display:flex;
  justify-content:center;
  align-items:center;
  min-height:100vh;
}
.container {
  width:95%;
  max-width:700px;
  padding:40px;
  background: var(--card);
  backdrop-filter: blur(20px);
  border-radius:16px;
  border:1px solid rgba(255,255,255,0.1);
  box-shadow:0 20px 40px rgba(0,0,0,0.4);
  text-align:center;
}
h1 { margin-bottom:5px; font-weight:600; letter-spacing:0.5px; }
.subtitle { color: var(--muted); font-size:14px; margin-bottom:30px; }
.controls { display:flex; flex-direction:column; gap:15px; }
select, button {
  padding:12px;
  font-size:15px;
  border-radius:8px;
  border:none;
}
select { background:#1e293b; color:var(--text);}
button { background:var(--accent); color:white; font-weight:500; cursor:pointer; transition:0.25s ease;}
button:hover { transform:translateY(-2px); box-shadow:0 8px 20px rgba(59,130,246,0.4);}
.study-section, .quiz-section, .summary-section {
  margin-top:30px;
  padding:20px;
  background: rgba(255,255,255,0.03);
  border-radius:12px;
  text-align:left;
  animation: fadeIn 0.3s ease;
  transition: background 0.25s ease;
}
.progress { font-size:12px; color:var(--muted); margin-bottom:5px; }
.progress-bar {
  height:6px;
  background:rgba(59,130,246,0.2);
  border-radius:3px;
  overflow:hidden;
  margin-bottom:10px;
}
.progress-fill {
  height:100%;
  width:0%;
  background: var(--accent);
  transition: width 0.25s ease;
}
.word { font-weight:600; font-size:20px; margin-bottom:5px;}
.definition { font-size:14px;}
.example { font-style:italic; font-size:13px; color:var(--muted); margin-bottom:15px;}
.quiz-item label { display:block; margin-bottom:5px;}
.quiz-item input {
  width:100%;
  padding:10px;
  border-radius:6px;
  border:none;
  font-size:16px;
  letter-spacing:1px;
  color: var(--text);
  background: #1e293b;
}
.correct-letter {
  color: var(--correct);
  font-weight:600;
  animation: pop 0.3s ease;
  display:inline-block;
}
.feedback { margin-top:5px; font-weight:500; }
.end-buttons { display:flex; flex-direction:column; gap:15px; margin-top:15px; }

@keyframes fadeIn { from {opacity:0; transform:translateY(5px);} to {opacity:1; transform:translateY(0);} }
@keyframes pop { 0% {transform:scale(1);} 50% {transform:scale(1.4);} 100% {transform:scale(1);} }