:root {
  --light-bg: #ffffff;
  --dark-bg: #ffffff;
  --light-surface: #ffffff;
  --dark-surface: #ffffff;
  --light-text-primary: #0a0a0a;
  --dark-text-primary: #0a0a0a;
  --light-text-secondary: #565656;
  --dark-text-secondary: #565656;
  --light-primary: #000000;
  --dark-primary: #000000;
  --light-primary-hover: #000000;
  --dark-primary-hover: #000000;
  --light-border: #000000;
  --dark-border: #000000;
  --light-error: #000000;
  --dark-error: #000000;
  --light-card-bg: #f5f5f5;
  --dark-card-bg: #f5f5f5;
  --light-disabled-bg: #e5e5e5;
  --dark-disabled-bg: #e5e5e5;
  --light-disabled-text: #777;
  --dark-disabled-text: #777;
  --light-shadow-color-1: rgba(0,0,0,0.06);
  --dark-shadow-color-1: rgba(0,0,0,0.06);
  --light-shadow-color-2: rgba(0,0,0,0.06);
  --dark-shadow-color-2: rgba(0,0,0,0.06);
  --light-focus-shadow-color: rgba(0, 0, 0, 0.2);
  --dark-focus-shadow-color: rgba(0, 0, 0, 0.2);
  --light-button-focus-shadow-color: rgba(0, 0, 0, 0.3);
  --dark-button-focus-shadow-color: rgba(0, 0, 0, 0.3);
  --light-button-text: #ffffff;
  --dark-button-text: #0a0a0a;
  --flashcard-width: 220px;
  --flashcard-height: 150px;
}

body {
  font-family: 'Google Sans', Roboto, Arial, sans-serif;
  margin: 0;
  background:
    repeating-linear-gradient(0deg, rgba(0,0,0,0.03), rgba(0,0,0,0.03) 1px, transparent 1px, transparent 24px),
    repeating-linear-gradient(90deg, rgba(0,0,0,0.03), rgba(0,0,0,0.03) 1px, transparent 1px, transparent 24px),
    light-dark(var(--light-bg), var(--dark-bg));
  background-attachment: fixed;
  color: light-dark(var(--light-text-primary), var(--dark-text-primary));
  display: flex;
  justify-content: center;
  align-items: flex-start;
  min-height: 100vh;
  padding: 20px;
  box-sizing: border-box;
}

.container { background-color: light-dark(var(--light-surface), var(--dark-surface)); padding: 40px; border-radius: 0; border: 1px solid light-dark(var(--light-border), var(--dark-border)); width: 90%; max-width: 800px; text-align: left; margin-top: 20px; }

.back { color: light-dark(var(--light-text-secondary), var(--dark-text-secondary)); text-decoration: none; padding: 8px 12px; border-radius: 0; border: 1px solid light-dark(var(--light-border), var(--dark-border)); background: light-dark(var(--light-surface), var(--dark-surface)); transition: transform .25s cubic-bezier(.16,1,.3,1); }
.back:hover { transform: translate(-4px, -4px); box-shadow: 6px 6px 0 #000; }

h1 {
  color: light-dark(var(--light-primary), var(--dark-primary));
  margin-bottom: 15px;
  font-size: 2em;
  font-weight: 500;
}

p {
  margin-bottom: 25px;
  color: light-dark(var(--light-text-secondary), var(--dark-text-secondary));
  line-height: 1.6;
}

textarea {
  width: calc(100% - 22px);
  padding: 15px;
  margin-bottom: 25px;
  border: 1px solid light-dark(var(--light-border), var(--dark-border));
  border-radius: 8px;
  font-size: 16px;
  min-height: 120px;
  background-color: light-dark(var(--light-bg), var(--dark-card-bg)); /* Use darker card bg for dark text area */
  color: light-dark(var(--light-text-primary), var(--dark-text-primary));
  resize: vertical;
  transition: border-color 0.3s ease, box-shadow 0.3s ease;
}

textarea:focus {
  outline: none;
  border-color: light-dark(var(--light-primary), var(--dark-primary));
  box-shadow: 0 0 0 2px light-dark(var(--light-focus-shadow-color), var(--dark-focus-shadow-color));
}

button {
  background-color: #000;
  color: #fff;
  padding: 14px 24px;
  border: 1px solid #000;
  border-radius: 0;
  cursor: pointer;
  font-size: 16px;
  font-weight: 800;
  transition: transform .25s cubic-bezier(.16,1,.3,1);
  box-shadow: none;
  margin-top: 8px;
}

button:hover { transform: translate(-4px, -4px); box-shadow: 6px 6px 0 #000; }

button:focus { outline: 2px solid #000; outline-offset: 2px; }

button:disabled { background-color: #e5e5e5; color: #777; cursor: not-allowed; box-shadow: none; transform: none; }

#generateButton { color: #fff !important; background-color: #000 !important; border-color: #000 !important; }

.error-message {
  color: light-dark(var(--light-error), var(--dark-error));
  margin-top: 20px;
  font-weight: 500;
  min-height: 1.5em;
}
.error-message.loading { color: #93c5fd; }
.error-message.success { color: #22c55e; }
.error-message.error { color: light-dark(var(--light-error), var(--dark-error)); }

.row { display: grid; grid-template-columns: 1fr 260px; gap: 20px; align-items: start; margin: 14px 0; }
@media (max-width: 720px) { .row { grid-template-columns: 1fr; } }
.hint { color: light-dark(var(--light-text-secondary), var(--dark-text-secondary)); font-size: 12px; margin-top: 6px; opacity: .85; }

.flashcards-container {
  display: flex;
  flex-wrap: wrap;
  gap: 25px;
  margin-top: 40px;
  justify-content: center;
  perspective: 1000px; /* Add perspective for 3D effect */
}

.files-info {
  margin-top: 10px;
  color: light-dark(var(--light-text-secondary), var(--dark-text-secondary));
  font-size: 0.92em;
}

.drop-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.55);
  display: none;
  align-items: center;
  justify-content: center;
  z-index: 1000;
  backdrop-filter: blur(2px);
}
.drop-overlay.show { display: flex; }
.drop-content {
  background: light-dark(var(--light-surface), var(--dark-surface));
  border: 2px dashed light-dark(var(--light-border), var(--dark-border));
  color: light-dark(var(--light-text-primary), var(--dark-text-primary));
  padding: 26px 30px;
  border-radius: 14px;
  text-align: center;
  box-shadow: 0 10px 30px light-dark(var(--light-shadow-color-1), var(--dark-shadow-color-1));
}
.drop-icon { font-size: 40px; margin-bottom: 8px; }
.drop-text { font-weight: 600; margin-bottom: 6px; }
.drop-hint { font-size: 13px; color: light-dark(var(--light-text-secondary), var(--dark-text-secondary)); }

.flashcard {
  background-color: transparent; /* Make the outer container transparent */
  width: var(--flashcard-width);
  height: var(--flashcard-height);
  border: none; /* Remove border from outer container */
  border-radius: 10px;
  cursor: pointer;
  perspective: 1000px; /* Add perspective for 3D effect */
  box-shadow: none; /* Remove shadow from outer container */
}

@keyframes cardEnter {
  0% { opacity: 0; transform: translateY(8px) scale(0.98); }
  100% { opacity: 1; transform: translateY(0) scale(1); }
}
.flashcard.enter { animation: cardEnter .35s ease both; }

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  text-align: center;
  transition: transform 0.6s;
  transform-style: preserve-3d;
  box-shadow: 0 1px 2px light-dark(var(--light-shadow-color-2), var(--dark-shadow-color-2)); /* Apply shadow here */
  border-radius: 10px; /* Apply border-radius here */
}

.flashcard.flipped .flashcard-inner {
  transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
  position: absolute;
  width: 100%;
  height: 100%;
  -webkit-backface-visibility: hidden; /* Safari */
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 20px; /* Reduced padding for content */
  box-sizing: border-box;
  border-radius: 10px; /* Match parent */
  border: 1px solid light-dark(var(--light-border), var(--dark-border)); /* Apply border here */
  background-color: light-dark(var(--light-card-bg), var(--dark-card-bg)); /* Apply background here */
}

.flashcard-back {
  transform: rotateY(180deg);
}

.flashcard:hover .flashcard-inner {
  box-shadow: 0 4px 8px light-dark(var(--light-shadow-color-1), var(--dark-shadow-color-1));
}

.flashcard:hover .flashcard-front,
.flashcard:hover .flashcard-back {
   border-color: light-dark(var(--light-primary), var(--dark-primary));
}


.term {
  font-size: 1.3em; /* Adjust size */
  font-weight: 500;
  color: light-dark(var(--light-text-primary), var(--dark-text-primary));
}

.definition {
  font-size: 1.0em; /* Adjust size */
  color: light-dark(var(--light-text-secondary), var(--dark-text-secondary));
  line-height: 1.4; /* Adjust line height */
}

/* Mobile refinements */
@media (max-width: 480px) {
  :root {
    --flashcard-width: 88vw;
    --flashcard-height: 180px;
  }
  .container { width: 96%; padding: 20px; }
  h1 { font-size: 1.6em; }
  .term { font-size: 1.15em; }
  .definition { font-size: 0.98em; }
  textarea { min-height: 100px; font-size: 15px; }
  button { width: 100%; }
}

footer {
  margin-top: 50px;
  padding-top: 25px;
  border-top: 1px solid light-dark(var(--light-border), var(--dark-border));
  color: light-dark(var(--light-text-secondary), var(--dark-text-secondary));
  font-size: 0.9em;
}