:root {
  --primary-color: #00a9e0; /* Brighter Azure Blue for contrast */
  --secondary-color: #0078d4;
  --background-color: #121212; /* Dark background */
  --card-background: #1e1e1e; /* Slightly lighter dark background for elements */
  --text-color: #e0e0e0; /* Light text */
  --text-color-light: #aaaaaa;
  --border-color: #333333;
  --success-color: #8bc34a; /* Green */
  --error-color: #ff5252; /* Red */
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: "Roboto", sans-serif;
}

body {
  background-color: var(--background-color);
  color: var(--text-color);
  line-height: 1.6;
}

/* --- Login Screen Styles --- */
#login-container {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: linear-gradient(135deg, #1e1e1e 0%, #000000 100%);
}

.login-card {
  background-color: var(--card-background);
  padding: 40px;
  border-radius: 12px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
  width: 90%;
  max-width: 400px;
  text-align: center;
}

.login-card h2 {
  color: var(--primary-color);
  margin-bottom: 25px;
}

.login-card input {
  width: 100%;
  padding: 12px;
  margin-bottom: 15px;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  font-size: 16px;
  background-color: #2c2c2c;
  color: var(--text-color);
}

.login-card button {
  width: 100%;
  padding: 12px;
  background-color: var(--primary-color);
  color: var(--card-background);
  border: none;
  border-radius: 6px;
  font-size: 18px;
  cursor: pointer;
  transition: background-color 0.2s;
}

.login-card button:hover {
  background-color: var(--secondary-color);
}

.credentials-info {
  margin-top: 20px;
  padding: 10px;
  background-color: #333333;
  border: 1px dashed var(--primary-color);
  border-radius: 6px;
  font-size: 0.9em;
  color: var(--text-color);
}

.error-message {
  color: var(--error-color);
  margin-top: 10px;
  font-weight: bold;
}

/* --- Main App Layout --- */
header {
  background-color: var(--card-background);
  padding: 15px 50px;
  border-bottom: 3px solid var(--primary-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

header h1 {
  font-size: 1.5em;
  color: var(--primary-color);
}

main {
  padding: 20px 50px;
  max-width: 1200px;
  margin: 0 auto;
}

.view {
  margin-top: 20px;
  padding: 20px;
  background-color: var(--card-background);
  border-radius: 8px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
}

/* Navigation Buttons */
.nav-btn {
  padding: 10px 15px;
  margin-left: 10px;
  background-color: var(--card-background);
  color: var(--primary-color);
  border: 1px solid var(--primary-color);
  border-radius: 4px;
  cursor: pointer;
  transition: all 0.2s;
}

.nav-btn:hover,
.nav-btn.active {
  background-color: var(--primary-color);
  color: var(--card-background);
}

/* --- Flashcard Styles --- */
.card-area {
  display: flex;
  flex-direction: column;
  align-items: center;
  margin-top: 20px;
}

.flashcard {
  width: 100%;
  max-width: 700px;
  min-height: 200px;
  background-color: #2c2c2c;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 30px;
  text-align: center;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.2);
  cursor: pointer;
  transition: transform 0.6s;
  perspective: 1000px;
  margin-bottom: 20px;
  font-size: 1.1em;
}

.card-back {
  text-align: left;
  white-space: pre-wrap;
}

.card-back strong {
  color: var(--primary-color);
}

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

.control-btn {
  padding: 10px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  transition: background-color 0.2s;
  font-size: 1em;
}

.control-btn:not(.primary) {
  background-color: #333333;
  color: var(--text-color);
}

.control-btn:hover:not(.primary) {
  background-color: #444444;
}

.primary {
  background-color: var(--primary-color) !important;
  color: var(--card-background);
}

.primary:hover {
  background-color: var(--secondary-color) !important;
}

.review-toggle.saved {
  background-color: #ffd700; /* Gold */
  color: var(--card-background);
  border: 1px solid #b8860b;
}

/* --- Quiz Input Area --- */
.quiz-length-input {
  margin: 20px 0;
}

.quiz-length-input label {
  display: block;
  margin-bottom: 5px;
  font-size: 1.1em;
}

.quiz-length-input input {
  padding: 10px;
  border: 1px solid var(--border-color);
  border-radius: 4px;
  background-color: #2c2c2c;
  color: var(--text-color);
  width: 150px;
  text-align: center;
}

/* --- Quiz Styles --- */
.question-text {
  font-size: 1.2em;
  font-weight: bold;
  margin-bottom: 20px;
  padding: 15px;
  border-left: 5px solid var(--primary-color);
  background-color: #2c2c2c;
}

.options-container {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 20px;
}

.quiz-option {
  padding: 15px;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  cursor: pointer;
  transition: background-color 0.2s, border-color 0.2s;
  text-align: left;
  background-color: #242424;
}

.quiz-option:hover {
  background-color: #333;
  border-color: var(--primary-color);
}

.quiz-option.selected {
  background-color: #3a3a3a;
  border-color: var(--secondary-color);
  font-weight: bold;
}

.quiz-option.correct {
  background-color: #1a3c1a; /* Darker success */
  border-color: var(--success-color);
  font-weight: bold;
}

.quiz-option.incorrect {
  background-color: #4a1a1a; /* Darker error */
  border-color: var(--error-color);
}

.quiz-controls {
  margin-top: 20px;
  text-align: right;
}

.feedback-box {
  margin-top: 15px;
  padding: 15px;
  border-radius: 6px;
  border-left: 5px solid;
  display: none;
  background-color: #242424;
}

.feedback-box.correct-feedback {
  border-color: var(--success-color);
  background-color: #1a3c1a;
}

.feedback-box.incorrect-feedback {
  border-color: var(--error-color);
  background-color: #4a1a1a;
}

/* --- Quiz Results Review --- */
.quiz-result-item {
  padding: 15px;
  margin-bottom: 10px;
  border-radius: 6px;
  border-left: 5px solid;
}

.result-correct {
  border-left-color: var(--success-color);
  background-color: #1a3c1a;
}

.result-incorrect {
  border-left-color: var(--error-color);
  background-color: #4a1a1a;
}

.quiz-result-item p {
  margin-bottom: 5px;
}
.quiz-result-item strong {
  display: block;
  margin-top: 5px;
}

/* --- Review View List --- */
#review-list-container h4 {
  color: var(--primary-color);
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 5px;
  margin-top: 15px;
}

.review-item {
  margin-bottom: 20px;
  padding: 15px;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background-color: #2c2c2c;
}

.review-item p {
  margin-bottom: 10px;
}

.review-item .explanation {
  margin-top: 10px;
  font-size: 0.9em;
  padding-top: 5px;
  border-top: 1px dotted #555;
  white-space: pre-wrap;
  color: var(--text-color-light);
}

@media (max-width: 768px) {
  header {
    flex-direction: column;
    text-align: center;
    padding: 10px 20px;
  }

  #main-nav {
    margin-top: 10px;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 5px;
  }

  .nav-btn {
    margin: 5px 0;
    flex-grow: 1;
  }

  main {
    padding: 20px;
  }

  .flashcard-controls {
    flex-direction: column;
  }

  .control-btn {
    width: 100%;
    margin-top: 5px;
  }
}