:root {
  --primary-color: #6200ee;
  --secondary-color: #03dac6;
  --background-color: #f5f5f5;
  --surface-color: #ffffff;
  --text-primary: #000000;
  --text-secondary: #757575;
}

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background-color: var(--background-color);
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.container {
  width: 90%;
  max-width: 500px;
  background-color: var(--surface-color);
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 4px 20px rgba(0,0,0,0.1);
  text-align: center;
}

h1 {
  color: var(--primary-color);
  margin-bottom: 2rem;
}

.card {
  min-height: 200px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  margin-bottom: 2rem;
  padding: 1.5rem;
  border: 1px solid #eee;
  border-radius: 8px;
  transition: transform 0.3s;
}

.word {
  font-size: 2.5rem;
  font-weight: bold;
  color: var(--primary-color);
  margin-bottom: 0.5rem;
}

.meaning {
  font-size: 1.2rem;
  color: var(--text-secondary);
  margin-bottom: 1.5rem;
  display: none;
}

.sentence {
  font-style: italic;
  font-size: 1.1rem;
  color: #444;
  line-height: 1.5;
}

.sentence .blank {
  color: var(--primary-color);
  text-decoration: underline;
  font-weight: bold;
}

.controls {
  display: flex;
  gap: 10px;
  justify-content: center;
  flex-wrap: wrap;
}

button {
  padding: 0.8rem 1.5rem;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  font-weight: 600;
  transition: opacity 0.2s;
}

.btn-primary {
  background-color: var(--primary-color);
  color: white;
}

.btn-secondary {
  background-color: var(--secondary-color);
  color: #000;
}

button:hover {
  opacity: 0.9;
}

button:disabled {
  background-color: #ccc;
  cursor: not-allowed;
}

.mode-toggle {
  margin-bottom: 1rem;
  display: flex;
  justify-content: flex-end;
}