:root {
  /* Paleta de colores técnica y moderna */
  --bg-primary: #f8fafc;
  /* Gris muy claro / Blanco */
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;

  --text-primary: #1e293b;
  /* Gris antracita */
  --text-secondary: #475569;
  --text-muted: #64748b;

  --accent-blue-solid: #0ea5e9;
  /* Azul sólido */
  --accent-blue-light: #e0f2fe;
  /* Azul celeste */
  --accent-blue-dark: #0369a1;
  /* Azul petróleo */

  --border-color: #e2e8f0;

  /* Estados de validación */
  --success: #10b981;
  --error: #ef4444;
  --error-bg: #fef2f2;
  --warning: #f59e0b;

  /* Espaciado y cuadrícula */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;

  --border-radius: 6px;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
}

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

body {
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.5;
  font-size: 15px;
}

/* Header */
.app-header {
  background-color: var(--bg-secondary);
  border-bottom: 1px solid var(--border-color);
  padding: var(--spacing-lg) var(--spacing-md);
  box-shadow: var(--shadow-sm);
  margin-bottom: var(--spacing-xl);
}

.header-container {
  max-width: 1400px;
  margin: 0 auto;
}

.app-header h1 {
  font-size: 1.5rem;
  color: var(--accent-blue-dark);
  font-weight: 600;
  letter-spacing: -0.025em;
}

.app-header p {
  color: var(--text-secondary);
  font-size: 0.875rem;
  margin-top: var(--spacing-xs);
}

/* Main Layout */
.app-main {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 var(--spacing-md) var(--spacing-xl);
}

.grid-container {
  display: grid;
  grid-template-columns: 320px 1fr 400px;
  gap: var(--spacing-lg);
  align-items: start;
}

/* Panels */
.panel {
  background-color: var(--bg-secondary);
  border-radius: var(--border-radius);
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.panel-header {
  background-color: var(--bg-tertiary);
  padding: var(--spacing-md) var(--spacing-lg);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.panel-header h2 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
}

.panel-content {
  padding: var(--spacing-lg);
  flex: 1;
}

/* Forms */
.form-group {
  margin-bottom: var(--spacing-md);
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-secondary);
  margin-bottom: var(--spacing-xs);
}

.form-control {
  width: 100%;
  padding: 0.5rem 0.75rem;
  font-family: 'Inter', sans-serif;
  font-size: 0.9rem;
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.form-control:focus {
  outline: none;
  border-color: var(--accent-blue-solid);
  box-shadow: 0 0 0 3px var(--accent-blue-light);
}

.input-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-lg);
}

/* Input Append (Units) */
.input-group {
  position: relative;
  display: flex;
  align-items: center;
}

.input-group .form-control {
  padding-right: 2.5rem;
  /* Space for unit */
}

.input-group-text {
  position: absolute;
  right: 1px;
  top: 1px;
  bottom: 1px;
  padding: 0 0.5rem;
  background-color: var(--bg-tertiary);
  border-left: 1px solid var(--border-color);
  border-top-right-radius: var(--border-radius);
  border-bottom-right-radius: var(--border-radius);
  color: var(--text-muted);
  font-size: 0.75rem;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 2.5rem;
}

/* Switches / Toggles */
.mode-switch {
  margin-bottom: var(--spacing-lg);
  padding: var(--spacing-sm);
  background-color: var(--accent-blue-light);
  border-radius: var(--border-radius);
  border: 1px solid var(--accent-blue-solid);
}

.switch-container {
  display: flex;
  align-items: center;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--accent-blue-dark);
  cursor: pointer;
}

.switch-container input {
  margin-right: var(--spacing-sm);
  accent-color: var(--accent-blue-solid);
}

/* Buttons */
.actions {
  display: flex;
  gap: var(--spacing-sm);
  margin-top: var(--spacing-lg);
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.5rem 1rem;
  font-family: inherit;
  font-size: 0.875rem;
  font-weight: 500;
  border-radius: var(--border-radius);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.15s ease;
  width: 100%;
}

.btn-primary {
  background-color: var(--accent-blue-solid);
  color: white;
}

.btn-primary:hover {
  background-color: var(--accent-blue-dark);
}

.btn-secondary {
  background-color: var(--bg-tertiary);
  color: var(--text-secondary);
  border-color: var(--border-color);
}

.btn-secondary:hover {
  background-color: #e2e8f0;
  color: var(--text-primary);
}

.btn-sm {
  padding: 0.25rem 0.5rem;
  font-size: 0.75rem;
  width: auto;
}

.btn-outline {
  background-color: transparent;
  border-color: var(--accent-blue-solid);
  color: var(--accent-blue-solid);
}

.btn-outline:hover {
  background-color: var(--accent-blue-light);
}

/* Panel Central (Procedimiento) */
.procedure-panel {
  min-height: 500px;
}

#procedure-content {
  overflow-y: auto;
  max-height: 80vh;
}

.empty-state {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100%;
  color: var(--text-muted);
  text-align: center;
  font-style: italic;
  padding: var(--spacing-xl);
}

/* Estilos de Pasos Matemáticos */
.math-step {
  margin-bottom: var(--spacing-lg);
  padding: var(--spacing-md);
  background-color: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
}

.math-step-title {
  font-weight: 600;
  color: var(--accent-blue-dark);
  margin-bottom: var(--spacing-sm);
  font-size: 0.9rem;
  border-bottom: 1px solid #e2e8f0;
  padding-bottom: 4px;
}

.katex-display {
  margin: 0.5em 0 !important;
  overflow-x: auto;
  overflow-y: hidden;
}

/* Panel Derecho (Gráficas) */
.visuals-grid {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
  max-height: 80vh;
  overflow-y: auto;
}

.visual-card {
  background-color: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  padding: var(--spacing-md);
}

.visual-card h3 {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Contenedores para Gráficos */
#phase-diagram {
  height: 200px;
  width: 100%;
  display: flex;
  position: relative;
  background-color: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: 4px;
  overflow: hidden;
}

#proportions-chart,
#e-n-chart,
#gamma-w-chart {
  width: 100% !important;
  max-height: 200px;
}

#cube-3d {
  width: 100%;
  height: 200px;
  background-color: #000;
  border-radius: 4px;
}

/* Simulador Saturador */
.simulator-card .slider-container {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xs);
}

.simulator-card label {
  font-size: 0.8rem;
  color: var(--text-secondary);
  display: flex;
  justify-content: space-between;
}

#s-value-display {
  font-weight: 600;
  color: var(--accent-blue-dark);
}

input[type=range] {
  width: 100%;
  accent-color: var(--accent-blue-solid);
}

/* Modal */
.modal {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 0, 0, 0.5);
  display: flex;
  justify-content: center;
  align-items: center;
  z-index: 1000;
}

.modal.hidden {
  display: none;
}

.modal-content {
  background-color: var(--bg-secondary);
  padding: var(--spacing-xl);
  border-radius: var(--border-radius);
  width: 100%;
  max-width: 500px;
  box-shadow: var(--shadow-md);
  position: relative;
}

.modal-content.warning {
  border-top: 4px solid var(--error);
}

.close-btn {
  position: absolute;
  top: var(--spacing-md);
  right: var(--spacing-md);
  cursor: pointer;
  font-size: 1.5rem;
  color: var(--text-muted);
  line-height: 1;
}

.modal-title {
  color: var(--error);
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
}

/* ============================================================
   MODO TOGGLE (Cálculo / Simulación)
   ============================================================ */
.app-mode-toggle {
  display: flex;
  gap: 0;
  border: 1px solid var(--accent-blue-solid);
  border-radius: var(--border-radius);
  overflow: hidden;
  margin-bottom: var(--spacing-lg);
}

.mode-option {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  padding: 0.45rem 0.5rem;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--accent-blue-dark);
  transition: background 0.15s, color 0.15s;
  background: #fff;
  user-select: none;
}

.mode-option:first-child {
  border-right: 1px solid var(--accent-blue-solid);
}

.mode-option input[type=radio] {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
  pointer-events: none;
}

.mode-option:has(input:checked) {
  background: var(--accent-blue-solid);
  color: #fff;
}

.mode-label {
  pointer-events: none;
}

/* ============================================================
   PANEL DE SIMULACIÓN
   ============================================================ */
.sim-info-box {
  background: #fffbeb;
  border: 1px solid #f59e0b;
  border-radius: var(--border-radius);
  padding: var(--spacing-sm) var(--spacing-md);
  font-size: 0.82rem;
  color: #78350f;
  margin-bottom: var(--spacing-md);
  line-height: 1.5;
}

.sim-panel {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.sim-panel label {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-secondary);
}

.sim-panel label strong {
  color: var(--accent-blue-dark);
}

.sim-results {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  padding: var(--spacing-md);
  max-height: 320px;
  overflow-y: auto;
}

.sim-placeholder {
  color: var(--text-muted);
  font-style: italic;
  font-size: 0.85rem;
  text-align: center;
  padding: var(--spacing-sm);
}

.sim-results-grid {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.sim-result-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 5px 8px;
  background: #fff;
  border-radius: 4px;
  border: 1px solid var(--border-color);
  font-size: 0.82rem;
}

.sim-lbl {
  color: var(--text-secondary);
  font-weight: 500;
}

.sim-val {
  color: var(--accent-blue-dark);
  font-weight: 600;
  font-family: 'Courier New', monospace;
}

/* ============================================================
   DIAGRAMA DE FASES — soporte SVG
   ============================================================ */
#phase-diagram {
  height: auto !important;
  min-height: 280px;
  overflow: visible !important;
  background: #fff !important;
}

#phase-diagram svg {
  display: block;
  width: 100%;
}

/* ============================================================
   SELECTOR DE UNIDADES
   ============================================================ */
.unit-selector-group {
  background: linear-gradient(135deg, #ede9fe, #dbeafe);
  border: 1px solid #7c3aed;
  border-radius: var(--border-radius);
  padding: var(--spacing-sm) var(--spacing-md);
  margin-bottom: var(--spacing-md);
}

.unit-selector-group label {
  color: #4c1d95 !important;
  font-weight: 600 !important;
  font-size: 0.875rem;
}

.unit-select {
  border-color: #7c3aed !important;
  background-color: #fff !important;
}

.unit-select:focus {
  border-color: #7c3aed !important;
  box-shadow: 0 0 0 3px rgba(124, 58, 237, 0.2) !important;
}

/* Unidades más largas (kN/m³, lb/ft³) necesitan más espacio */
.input-group-text {
  width: auto !important;
  min-width: 2.5rem;
  white-space: nowrap;
  font-size: 0.72rem;
}

/* ============================================================
   HIDDEN UTILITY
   ============================================================ */
.hidden {
  display: none !important;
}

/* ============================================================
   INPUTS DESACTIVADOS
   ============================================================ */
.form-control:disabled {
  background-color: var(--bg-tertiary);
  color: var(--text-muted);
  cursor: not-allowed;
}

/* Responsividad */
@media (max-width: 1200px) {
  .grid-container {
    grid-template-columns: 1fr;
  }

  .visuals-grid {
    flex-direction: row;
    flex-wrap: wrap;
    max-height: none;
    overflow: visible;
  }

  .visual-card {
    flex: 1 1 calc(50% - var(--spacing-md));
    min-width: 300px;
  }

  #procedure-content {
    max-height: 50vh;
  }
}