@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap');

:root {
  --primary: #6366f1;
  --primary-hover: #4f46e5;
  --bg: #0f172a;
  --card-bg: rgba(30, 41, 59, 0.7);
  --card-border: rgba(255, 255, 255, 0.1);
  --surface: #1e293b;
  --surface-hover: #334155;
  --text: #f8fafc;
  --text-muted: #94a3b8;
  --accent: #818cf8;
  --accent-hover: #c084fc;
  --success: #22c55e;
  --error: #ef4444;
  --border: #334155;
  --radius: 12px;
  --glass: blur(12px);
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: 'Inter', sans-serif;
  background: radial-gradient(circle at top left, #1e1b4b, #0f172a);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.5;
}

/* Custom Scrollbar */
::-webkit-scrollbar {
  width: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg);
}

::-webkit-scrollbar-thumb {
  background: var(--surface);
  border-radius: 10px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--primary);
}

.app {
  max-width: 1400px;
  margin: 0 auto;
  padding: 2rem;
  animation: fadeIn 0.5s ease-out;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.hidden {
  display: none !important;
}

/* Header */
.header {
  text-align: center;
  margin-bottom: 3rem;
}

.header h1 {
  font-size: 2.25rem;
  font-weight: 800;
  margin-bottom: 0.5rem;
  background: linear-gradient(to right, #818cf8, #c084fc);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.header p {
  color: var(--text-muted);
  font-size: 1.125rem;
}

.header-top {
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 1000px;
  margin: 0 auto 1.5rem;
  padding: 1rem 1.5rem;
  background: var(--card-bg);
  backdrop-filter: var(--glass);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
}

.user-menu {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

#usernameDisplay {
  font-weight: 600;
  color: var(--accent);
}

#adminLink {
  color: var(--text-muted);
  text-decoration: none;
  padding: 0.5rem 1rem;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  transition: all 0.2s;
}

#adminLink:hover {
  background: var(--surface-hover);
  color: var(--text);
  border-color: var(--accent);
}

/* Upload */
.upload-section {
  max-width: 640px;
  margin: 0 auto 3rem;
}

.upload-zone {
  background: var(--card-bg);
  backdrop-filter: var(--glass);
  border: 2px dashed var(--card-border);
  border-radius: 20px;
  padding: 4rem 2rem;
  text-align: center;
  cursor: pointer;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.upload-zone:hover,
.upload-zone.dragover {
  border-color: var(--primary);
  background: rgba(99, 102, 241, 0.1);
  transform: scale(1.02);
}

.upload-zone .link {
  color: var(--primary);
  font-weight: 600;
  text-decoration: none;
}

.uploaded-files {
  margin-top: 2rem;
}

.uploaded-files h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.uploaded-files-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 1rem;
}

.file-item {
  background: var(--card-bg);
  padding: 1rem;
  border-radius: var(--radius);
  border: 1px solid var(--card-border);
  color: var(--text);
  text-decoration: none;
  font-size: 0.875rem;
  transition: all 0.2s;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.file-item:hover {
  background: var(--primary);
  border-color: var(--primary);
  transform: translateY(-2px);
}

/* Toolbar */
.toolbar {
  background: var(--card-bg);
  backdrop-filter: var(--glass);
  padding: 1rem 1.5rem;
  border-radius: var(--radius);
  border: 1px solid var(--card-border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 2rem;
  gap: 1rem;
}

.btn {
  padding: 0.625rem 1.25rem;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}

.btn:hover {
  background: var(--surface-hover);
  border-color: var(--accent);
}

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

.btn-primary {
  background: linear-gradient(to right, var(--primary), #8b5cf6);
  border: none;
  color: white;
}

.btn-primary:hover {
  filter: brightness(1.1);
  transform: translateY(-1px);
}

.btn:disabled {
  opacity: 0.6;
  cursor: not-allowed;
  filter: grayscale(0.5);
  transform: none !important;
}

.btn-ghost {
  background: transparent;
  border: none;
}

.btn-sm {
  padding: 0.375rem 0.75rem;
  font-size: 0.75rem;
}

/* Content wrapper */
.content-wrapper {
  display: grid;
  grid-template-columns: 1fr 480px;
  gap: 2.5rem;
  min-height: 600px;
}

/* PDF Viewer */
.pdf-container {
  background: var(--card-bg);
  border-radius: var(--radius);
  border: 1px solid var(--card-border);
  overflow: auto;
  max-height: 85vh;
  position: relative;
}

.pdf-viewer {
  padding: 2rem;
}

/* Side panel */
.side-panel {
  background: var(--card-bg);
  backdrop-filter: var(--glass);
  border-radius: var(--radius);
  border: 1px solid var(--card-border);
  padding: 2rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
  overflow-y: auto;
  max-height: 85vh;
}

.side-panel .explanation {
  background: rgba(15, 23, 42, 0.4);
  padding: 1.75rem;
  border-radius: var(--radius);
  border: 1px solid var(--card-border);
  line-height: 1.7;
  font-size: 1.05rem;
  color: #e2e8f0;
}

.explanation p,
.explanation ul,
.explanation ol {
  margin-bottom: 1.25rem;
}

.explanation li {
  margin-bottom: 0.75rem;
}

.explanation li:last-child {
  margin-bottom: 0;
}

.side-panel h3 {
  color: var(--accent);
  margin-bottom: 1.25rem;
  font-size: 1.5rem;
  font-weight: 700;
}

/* Markdown Styling in Side Panel */
.explanation h3 {
  font-size: 1.25rem;
  color: var(--accent);
  margin: 1.5rem 0 1rem;
}

.explanation h4 {
  font-size: 1.1rem;
  color: var(--text);
  margin: 1.25rem 0 0.75rem;
}

.explanation p {
  margin-bottom: 1.25rem;
}

.explanation ul,
.explanation ol {
  margin-left: 1.5rem;
  margin-bottom: 1.25rem;
}

.explanation li {
  margin-bottom: 0.5rem;
}

.explanation strong {
  color: #fff;
  font-weight: 700;
}

.explanation hr {
  border: 0;
  border-top: 1px solid var(--card-border);
  margin: 1.5rem 0;
}

.highlight-red {
  color: #fb7185;
  background: rgba(251, 113, 133, 0.1);
  padding: 0 4px;
  border-radius: 4px;
  font-weight: 600;
}

/* Exercises */
.exercise-card {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 16px;
  padding: 1.5rem;
  margin-bottom: 1.5rem;
  animation: slideIn 0.3s ease-out;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateX(20px);
  }

  to {
    opacity: 1;
    transform: translateX(0);
  }
}

.option {
  background: var(--surface);
  border: 1px solid var(--border);
  padding: 1rem;
  border-radius: var(--radius);
  margin-top: 0.75rem;
  transition: all 0.2s;
}

.option:hover {
  background: var(--surface-hover);
  border-color: var(--primary);
}

.option.selected {
  background: rgba(99, 102, 241, 0.1);
  border-color: var(--primary);
}

.option.correct {
  background: rgba(34, 197, 94, 0.1);
  border-color: var(--success);
}

.option.wrong {
  background: rgba(239, 68, 68, 0.1);
  border-color: var(--error);
}

/* Popups */
.explanation-popup-content {
  background: #1e293b;
  border-radius: 20px;
  border: 1px solid var(--card-border);
  padding: 2.5rem;
  box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
  max-width: 600px;
  width: 90%;
  line-height: 1.7;
  font-size: 1.1rem;
}

.explanation-popup-content h3 {
  color: var(--accent);
  margin-bottom: 1.5rem;
}

/* Loading */
.loading-overlay {
  background: rgba(15, 23, 42, 0.8);
  backdrop-filter: blur(4px);
}

.spinner {
  border-top-color: var(--primary);
}