:root {
  --primary-color: #3498db; /* A vibrant blue */
  --background-color: #1a1d28;
  --card-background: #252936;
  --text-color: #f0f0f0;
  --text-secondary: #bdc3c7;
  --correct-color: #2ecc71;
  --wrong-color: #e74c3c;
  --hover-border: rgba(52, 152, 219, 0.5);
}

body {
  font-family: "Poppins", sans-serif;
  background-color: var(--background-color);
  color: var(--text-color);
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 20px;
  box-sizing: border-box;
}

.hidden {
  display: none;
}

.app-container {
  width: 100%;
  max-width: 600px;
  background: var(--card-background);
  border-radius: 15px;
  padding: 30px 40px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
  text-align: center;
}

button {
  background-color: #007bff;
  color: white;
  border: none;
  padding: 10px 20px;
  font-size: 16px;
  cursor: pointer;
  margin-top: 10px;
}

h1 {
  margin-top: 0;
  color: var(--primary-color);
}

h2 {
  font-size: 1.5rem;
  font-weight: 600;
  min-height: 80px;
}

.subtitle {
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin-bottom: 30px;
}

.difficulty-selection {
  display: flex;
  flex-direction: column;
  gap: 15px;
  margin-top: 20px;
}

/* --- Button Styling --- */
.btn {
  background-color: var(--primary-color);
  color: white;
  border: none;
  padding: 12px 25px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  margin-top: 10px;
  border-radius: 8px;
  transition:
    transform 0.2s ease,
    box-shadow 0.2s ease;
}

.btn:hover {
  transform: translateY(-3px);
  box-shadow: 0 4px 15px rgba(52, 152, 219, 0.4);
}

/* --- Options Styling --- */
#options {
  display: flex;
  flex-direction: column;
  gap: 15px;
  margin-top: 20px;
}

.option {
  padding: 15px;
  background: rgba(255, 255, 255, 0.05);
  cursor: pointer;
  border-radius: 8px;
  border: 2px solid transparent;
  text-align: left;
  transition: all 0.3s ease;
  position: relative;
}

.option:hover {
  border-color: var(--hover-border);
  background: rgba(255, 255, 255, 0.1);
}

/* --- Correct/Wrong Answer Feedback --- */
.option.correct {
  background-color: var(--correct-color);
  color: white;
  border-color: var(--correct-color);
}

.option.wrong {
  background-color: var(--wrong-color);
  color: white;
  border-color: var(--wrong-color);
}

/* Add icons for feedback */
.option.correct::after,
.option.wrong::after {
  font-size: 1.2rem;
  font-weight: bold;
  position: absolute;
  right: 15px;
  top: 50%;
  transform: translateY(-50%);
}

.option.correct::after {
  content: "✔";
}

.option.wrong::after {
  content: "✖";
}

/* Disable pointer events after an answer is selected */
.options-disabled .option {
  pointer-events: none;
}

/* --- Progress Bar Styling --- */
#progress-container {
  width: 100%;
  height: 8px;
  background-color: rgba(0, 0, 0, 0.3);
  border-radius: 4px;
  margin-bottom: 5px;
}

#progress-bar {
  height: 100%;
  width: 0%; /* Initially 0, updated by JS */
  background-color: var(--primary-color);
  border-radius: 4px;
  transition: width 0.4s ease-in-out;
}

#progress-text {
  font-size: 0.9rem;
  color: var(--text-secondary);
  margin-bottom: 20px;
}