:root {
  --color-bg: #f8fafc;
  --color-surface: #ffffff;
  --color-surface-subtle: #f1f5f9;
  --color-border: #e2e8f0;
  --color-border-strong: #cbd5e1;
  --color-text-main: #0f172a;
  --color-text-muted: #475569;
  --color-text-subtle: #64748b;
  --color-primary: #1e293b;
  --color-primary-hover: #0f172a;
  --color-accent: #2563eb;
  --color-accent-subtle: #eff6ff;
  --color-success: #15803d;
  --color-success-bg: #f0fdf4;
  --color-success-border: #bbf7d0;
  --color-error: #b91c1c;
  --color-error-bg: #fef2f2;
  --color-error-border: #fecaca;
  --color-warning: #b45309;
  --color-warning-bg: #fffbeb;
  --color-code-bg: #0f172a;
  --color-code-text: #f8fafc;
  
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  
  --radius-sm: 4px;
  --radius-md: 6px;
  --radius-lg: 8px;
  
  --shadow-subtle: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-card: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px -1px rgba(0, 0, 0, 0.1);
  --shadow-focus: 0 0 0 3px rgba(37, 99, 235, 0.25);
  
  --container-max-w: 860px;
}

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

html {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.5;
  color: var(--color-text-main);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.skip-link {
  position: absolute;
  top: -40px;
  left: 1rem;
  background: var(--color-primary);
  color: #fff;
  padding: 0.5rem 1rem;
  z-index: 1000;
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: top 0.2s ease;
}

.skip-link:focus {
  top: 1rem;
}

.app-header {
  background-color: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  padding: 1.25rem 1.5rem;
}

.app-header__inner {
  max-width: var(--container-max-w);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.app-brand-wrapper {
  display: flex;
  align-items: center;
  gap: 0.85rem;
}

.app-brand-logo {
  border-radius: var(--radius-md);
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
  flex-shrink: 0;
}

.app-brand {
  font-size: 1.1rem;
  font-weight: 700;
  letter-spacing: -0.025em;
  color: var(--color-text-main);
  text-transform: uppercase;
  line-height: 1.2;
}

.app-motto {
  font-size: 0.775rem;
  font-weight: 600;
  color: var(--color-text-subtle);
  letter-spacing: 0.01em;
  margin-top: 0.15rem;
}

.app-brand-badge {
  display: inline-block;
  font-size: 0.725rem;
  font-weight: 600;
  padding: 0.125rem 0.45rem;
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border);
  color: var(--color-text-muted);
  border-radius: var(--radius-sm);
  margin-left: 0.4rem;
  vertical-align: middle;
  text-transform: none;
}

.footer-motto {
  font-size: 0.9rem;
  color: var(--color-text-main);
  margin-bottom: 0.35rem;
}

.main-content {
  flex: 1;
  max-width: var(--container-max-w);
  width: 100%;
  margin: 2rem auto;
  padding: 0 1.25rem;
}

/* Card base */
.card {
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  padding: 2rem;
  margin-bottom: 2rem;
}

/* Typography elements */
.h1-title {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text-main);
  margin-bottom: 0.5rem;
  line-height: 1.25;
}

.text-muted {
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

.text-subtle {
  color: var(--color-text-subtle);
  font-size: 0.85rem;
}

/* Forms */
.form-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.25rem;
  margin-top: 1.5rem;
}

@media (min-width: 640px) {
  .form-grid-2col {
    grid-template-columns: repeat(2, 1fr);
  }
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.375rem;
}

.form-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--color-text-main);
}

.form-input,
.form-select,
.form-textarea {
  width: 100%;
  font-family: inherit;
  font-size: 0.95rem;
  padding: 0.65rem 0.85rem;
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-md);
  background-color: var(--color-surface);
  color: var(--color-text-main);
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.form-input:focus,
.form-select:focus,
.form-textarea:focus {
  outline: none;
  border-color: var(--color-accent);
  box-shadow: var(--shadow-focus);
}

.form-input[readonly] {
  background-color: var(--color-surface-subtle);
  color: var(--color-text-muted);
  cursor: not-allowed;
}

.form-hint {
  font-size: 0.775rem;
  color: var(--color-text-subtle);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-family: inherit;
  font-size: 0.95rem;
  font-weight: 600;
  padding: 0.75rem 1.5rem;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.15s ease;
  text-decoration: none;
}

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

.btn-primary:hover:not(:disabled) {
  background-color: var(--color-primary-hover);
}

.btn-secondary {
  background-color: var(--color-surface);
  border-color: var(--color-border-strong);
  color: var(--color-text-main);
}

.btn-secondary:hover:not(:disabled) {
  background-color: var(--color-surface-subtle);
}

.btn:disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

.btn-full {
  width: 100%;
}

/* Sticky Exam Header Bar */
.exam-sticky-bar {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-border);
  padding: 0.85rem 1.25rem 0.65rem 1.25rem;
  margin: -2rem -1.25rem 1.75rem -1.25rem;
  box-shadow: 0 4px 14px rgba(15, 23, 42, 0.08);
  transition: box-shadow 0.2s ease;
}

.exam-bar-inner {
  max-width: var(--container-max-w);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.exam-info-pill {
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--color-text-muted);
}

.exam-timer {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  font-weight: 700;
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-sm);
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border-strong);
  color: var(--color-text-main);
}

.exam-timer.timer-warning {
  background-color: var(--color-warning-bg);
  border-color: var(--color-warning);
  color: var(--color-warning);
  animation: pulse-border 1.5s infinite;
}

.exam-timer.timer-danger {
  background-color: var(--color-error-bg);
  border-color: var(--color-error);
  color: var(--color-error);
  animation: pulse-border 0.8s infinite;
}

@keyframes pulse-border {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.65; }
}

/* Progress bar */
.progress-container {
  width: 100%;
  height: 6px;
  background-color: var(--color-border);
  border-radius: 999px;
  overflow: hidden;
  margin-top: 0.5rem;
}

.progress-bar-fill {
  height: 100%;
  background-color: var(--color-accent);
  width: 0%;
  transition: width 0.25s ease;
}

/* Question Items */
.question-item {
  margin-bottom: 2rem;
  border-left: 3px solid var(--color-border-strong);
  padding-left: 1.25rem;
  padding-top: 0.25rem;
  padding-bottom: 0.25rem;
}

.question-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 1rem;
  margin-bottom: 0.75rem;
}

.question-number {
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--color-text-subtle);
}

.question-category-tag {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.2rem 0.5rem;
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
}

.question-statement {
  font-size: 1.05rem;
  font-weight: 600;
  line-height: 1.4;
  color: var(--color-text-main);
  margin-bottom: 1rem;
}

/* Code Snippet Block */
.code-block {
  background-color: var(--color-code-bg);
  color: var(--color-code-text);
  font-family: var(--font-mono);
  font-size: 0.875rem;
  line-height: 1.6;
  padding: 1rem 1.25rem;
  border-radius: var(--radius-md);
  margin-bottom: 1.25rem;
  overflow-x: auto;
  border: 1px solid #1e293b;
}

.code-block code {
  font-family: inherit;
  white-space: pre;
}

/* Options list */
.options-group {
  display: flex;
  flex-direction: column;
  gap: 0.65rem;
  margin-bottom: 1rem;
}

.option-label {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all 0.15s ease;
  font-size: 0.95rem;
  user-select: none;
}

.option-label:hover {
  background-color: var(--color-surface-subtle);
  border-color: var(--color-border-strong);
}

.option-input {
  margin-top: 0.25rem;
  accent-color: var(--color-accent);
  width: 1.1rem;
  height: 1.1rem;
  cursor: pointer;
}

.option-label:has(.option-input:checked) {
  border-color: var(--color-accent);
  background-color: var(--color-accent-subtle);
}

/* Justification box */
.justification-box {
  margin-top: 1rem;
  padding: 1rem;
  background-color: var(--color-surface-subtle);
  border: 1px dashed var(--color-border-strong);
  border-radius: var(--radius-md);
}

.justification-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-main);
  margin-bottom: 0.35rem;
}

/* Results view */
.results-scorecard {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
  margin-bottom: 2rem;
}

@media (min-width: 640px) {
  .results-scorecard {
    grid-template-columns: 240px 1fr;
  }
}

.score-main {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 2rem 1.5rem;
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  text-align: center;
}

.score-number {
  font-size: 3.5rem;
  font-weight: 800;
  line-height: 1;
  font-family: var(--font-mono);
  color: var(--color-text-main);
}

.score-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-subtle);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 0.5rem;
}

.score-status-badge {
  margin-top: 0.75rem;
  font-size: 0.8rem;
  font-weight: 600;
  padding: 0.25rem 0.75rem;
  border-radius: 999px;
}

.status-approved {
  background-color: var(--color-success-bg);
  color: var(--color-success);
  border: 1px solid var(--color-success-border);
}

.status-needs-review {
  background-color: var(--color-error-bg);
  color: var(--color-error);
  border: 1px solid var(--color-error-border);
}

/* Skill Breakdown */
.skills-grid {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  justify-content: center;
}

.skill-row {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

.skill-header {
  display: flex;
  justify-content: space-between;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-main);
}

.skill-bar-bg {
  height: 8px;
  background-color: var(--color-border);
  border-radius: 999px;
  overflow: hidden;
}

.skill-bar-fill {
  height: 100%;
  border-radius: 999px;
  background-color: var(--color-accent);
}

/* Feedback Breakdown Items */
.feedback-card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin-bottom: 1rem;
}

.feedback-card.correct {
  border-left: 4px solid var(--color-success);
}

.feedback-card.incorrect {
  border-left: 4px solid var(--color-error);
}

.feedback-badge {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
  margin-bottom: 0.5rem;
}

.feedback-badge.badge-correct {
  background-color: var(--color-success-bg);
  color: var(--color-success);
}

.feedback-badge.badge-incorrect {
  background-color: var(--color-error-bg);
  color: var(--color-error);
}

.remedial-box {
  margin-top: 0.75rem;
  padding: 0.75rem 1rem;
  background-color: var(--color-surface-subtle);
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  color: var(--color-text-muted);
}

.remedial-box strong {
  color: var(--color-text-main);
}

/* Student & Meta Information summary block */
.meta-summary-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.875rem;
  margin-bottom: 1.5rem;
}

.meta-summary-table th,
.meta-summary-table td {
  padding: 0.6rem 0.85rem;
  text-align: left;
  border-bottom: 1px solid var(--color-border);
}

.meta-summary-table th {
  color: var(--color-text-subtle);
  font-weight: 600;
  width: 35%;
  background-color: var(--color-surface-subtle);
}

.meta-summary-table td {
  color: var(--color-text-main);
}

/* Footer */
.app-footer {
  border-top: 1px solid var(--color-border);
  background-color: var(--color-surface);
  padding: 1.5rem;
  text-align: center;
  font-size: 0.8rem;
  color: var(--color-text-subtle);
  margin-top: auto;
}

/* Helpers */
.hidden {
  display: none !important;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* ==========================================================================
   Custom Modal / Alert System (Reemplaza diálogos nativos de Windows)
   ========================================================================== */
.custom-modal-backdrop {
  position: fixed;
  inset: 0;
  z-index: 9999;
  background-color: rgba(15, 23, 42, 0.45);
  backdrop-filter: blur(3px);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.25rem;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s ease-out;
}

.custom-modal-backdrop.modal-visible {
  opacity: 1;
  pointer-events: auto;
}

.custom-modal-card {
  background-color: var(--color-surface);
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-lg);
  box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.15), 0 8px 10px -6px rgba(0, 0, 0, 0.1);
  width: 100%;
  max-width: 480px;
  padding: 1.5rem;
  transform: scale(0.96) translateY(8px);
  transition: transform 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

.custom-modal-backdrop.modal-visible .custom-modal-card {
  transform: scale(1) translateY(0);
}

.custom-modal-header {
  margin-bottom: 0.75rem;
}

.custom-modal-badge {
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
  display: inline-block;
  margin-bottom: 0.4rem;
}

.modal-type-info .custom-modal-badge {
  background-color: var(--color-accent-subtle);
  color: var(--color-accent);
}

.modal-type-warning .custom-modal-badge {
  background-color: var(--color-warning-bg);
  color: var(--color-warning);
}

.modal-type-error .custom-modal-badge,
.modal-type-danger .custom-modal-badge {
  background-color: var(--color-error-bg);
  color: var(--color-error);
}

.modal-type-question .custom-modal-badge {
  background-color: var(--color-surface-subtle);
  color: var(--color-text-main);
  border: 1px solid var(--color-border);
}

.custom-modal-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-text-main);
  line-height: 1.3;
}

.custom-modal-message {
  font-size: 0.925rem;
  color: var(--color-text-muted);
  line-height: 1.5;
  margin-bottom: 1.5rem;
}

.custom-modal-footer {
  display: flex;
  justify-content: flex-end;
  gap: 0.75rem;
}

/* ==========================================================================
   Selector Interactivo de Exámenes (Elección del Estudiante)
   ========================================================================== */
.exam-cards-grid {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  margin-top: 0.5rem;
}

.exam-choice-card {
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  padding: 1rem 1.15rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background-color: var(--color-surface);
  cursor: pointer;
  transition: all 0.15s ease;
  user-select: none;
}

.exam-choice-card:hover {
  border-color: var(--color-border-strong);
  background-color: var(--color-surface-subtle);
}

.exam-choice-card:has(input:checked) {
  border-color: var(--color-accent);
  background-color: var(--color-accent-subtle);
  box-shadow: 0 0 0 1px var(--color-accent);
}

.exam-choice-radio {
  margin-top: 0.25rem;
  accent-color: var(--color-accent);
  width: 1.15rem;
  height: 1.15rem;
}

.exam-choice-content {
  flex: 1;
}

.exam-choice-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin-bottom: 0.25rem;
}

.exam-choice-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--color-text-main);
}

.exam-meta-pill {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.15rem 0.5rem;
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
}

.exam-choice-desc {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  line-height: 1.4;
}

.exam-preview-panel {
  margin-top: 1rem;
  padding: 1rem 1.25rem;
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.exam-preview-panel h3 {
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--color-text-subtle);
  margin-bottom: 0.4rem;
}

.exam-category-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 0.5rem;
}

.exam-category-chip {
  font-size: 0.75rem;
  padding: 0.2rem 0.55rem;
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 999px;
  color: var(--color-text-muted);
}

/* ==========================================================================
   Header Actions & GitHub Open Source Link
   ========================================================================== */
.header-actions {
  display: flex;
  align-items: center;
}

.github-pill-link {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--color-text-main);
  background-color: var(--color-surface-subtle);
  border: 1px solid var(--color-border);
  padding: 0.35rem 0.75rem;
  border-radius: 999px;
  text-decoration: none;
  transition: all 0.15s ease;
}

.github-pill-link:hover {
  background-color: #0f172a;
  color: #ffffff;
  border-color: #0f172a;
}

.github-icon {
  flex-shrink: 0;
}

/* ==========================================================================
   Mobile-First & Fluid Responsive Optimizations
   ========================================================================== */
html, body {
  /* overflow-x: clip previene desbordamiento horizontal SIN anular el comportamiento sticky */
  overflow-x: clip;
}

/* Prevenir auto-zoom en iOS Safari en campos de texto */
@media (max-width: 768px) {
  .form-input,
  .form-select,
  .form-textarea {
    font-size: 16px !important;
  }
}

/* Pantallas pequeñas (Móviles: 320px a 640px) */
@media (max-width: 640px) {
  .app-header {
    padding: 1rem;
  }

  .app-header__inner {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.75rem;
  }

  .header-actions {
    width: 100%;
    justify-content: flex-start;
  }

  .app-brand {
    font-size: 1rem;
  }

  .app-motto {
    font-size: 0.725rem;
  }

  .main-content {
    margin: 1rem auto;
    padding: 0 0.75rem;
  }

  .card {
    padding: 1.25rem 1rem;
    margin-bottom: 1.25rem;
    border-radius: var(--radius-md);
  }

  .h1-title {
    font-size: 1.25rem;
  }

  .exam-sticky-bar {
    top: 0;
    margin: -1rem -0.75rem 1.25rem -0.75rem;
    padding: 0.65rem 0.75rem 0.5rem 0.75rem;
    box-shadow: 0 4px 12px rgba(15, 23, 42, 0.08);
  }

  .exam-bar-inner {
    flex-direction: column;
    align-items: stretch;
    gap: 0.5rem;
  }

  .exam-bar-inner > div:last-child {
    display: flex;
    justify-content: space-between;
    width: 100%;
  }

  .exam-timer {
    font-size: 0.95rem;
    padding: 0.25rem 0.6rem;
  }

  .question-item {
    padding-left: 0.75rem;
    margin-bottom: 1.5rem;
  }

  .question-statement {
    font-size: 0.95rem;
  }

  .option-label {
    padding: 0.65rem 0.75rem;
    font-size: 0.9rem;
  }

  .code-block {
    padding: 0.75rem;
    font-size: 0.8rem;
    -webkit-overflow-scrolling: touch;
  }

  .results-scorecard {
    grid-template-columns: 1fr;
    gap: 1rem;
  }

  .score-number {
    font-size: 2.75rem;
  }

  .meta-summary-table {
    font-size: 0.8rem;
  }

  .meta-summary-table th,
  .meta-summary-table td {
    padding: 0.45rem 0.6rem;
  }

  .custom-modal-card {
    padding: 1.25rem 1rem;
  }

  .custom-modal-footer {
    flex-direction: column-reverse;
    gap: 0.5rem;
  }

  .custom-modal-footer .btn {
    width: 100%;
  }
}