:root {
  /* Modo claro */
  --bg-color: #ffffff;
  --text-color: #333333;
  --nav-bg: linear-gradient(45deg, #ffffff 0%, #f1f1f1 100%);
  --footer-bg: linear-gradient(135deg, #ffffff 0%, #e0e0e0 100%);
  --hover-color: #007bff;
  --icon-color: #333333;
  --transition-time: 0.3s;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  --menu-width: 280px;
}

[data-theme="dark"] {
  /* Modo oscuro */
  --bg-color: #121212;
  --text-color: #f8f9fa;
  --nav-bg: linear-gradient(45deg, #212529 0%, #4dabf7 100%);
  --footer-bg: linear-gradient(135deg, #212529 0%, #4dabf7 100%);
  --hover-color: #4dabf7;
  --icon-color: #f8f9fa;
  --shadow: 0 2px 8px rgba(255, 255, 255, 0.1);
}

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

/* Estructura base */
body {
  background-color: var(--bg-color);
  color: var(--text-color);
  font-family: 'Segoe UI', system-ui, sans-serif;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background-color var(--transition-time), color var(--transition-time);
  position: relative;
  overflow-x: hidden;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem;
  flex: 1;
}

/* Accesibilidad */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: var(--hover-color);
  color: var(--icon-color);
  padding: 8px;
  z-index: 1001;
  transition: top var(--transition-time);
}
.skip-link:focus {
  top: 0;
}

/* Header y logo */
header {
  text-align: center;
  padding: 2rem;
  background: var(--nav-bg);
}

.logo {
  width: 150px;
  height: auto;
  transition: transform var(--transition-time);
}
.logo:hover {
  transform: scale(1.05);
}

/* Navbar */
.navbar {
  background: var(--nav-bg);
  background-size: 200% 200%;
  animation: gradient-animation 3s infinite alternate;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 2rem;
  box-shadow: var(--shadow);
  position: sticky;
  top: 0;
  z-index: 1000;
}

@keyframes gradient-animation {
  0% {
    background-position: 0% 50%;
  }
  100% {
    background-position: 100% 50%;
  }
}

/* Navegación */
.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  color: var(--text-color);
  text-decoration: none;
  padding: 0.5rem 1rem;
  border-radius: 4px;
  transition: all var(--transition-time);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.nav-links a:hover,
.nav-links a:focus {
  background: rgba(0, 0, 0, 0.1);
  outline: none;
}

/* Menú móvil */
.menu-icon {
  display: none;
  background: none;
  border: none;
  color: var(--icon-color);
  font-size: 1.5rem;
  cursor: pointer;
  transition: color var(--transition-time);
}
.menu-icon:hover {
  color: var(--hover-color);
}

.mobile-menu {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: var(--nav-bg);
  z-index: 2000;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  transform: translateX(-100%);
  transition: transform var(--transition-time) ease-in-out;
}
.mobile-menu.active {
  transform: translateX(0);
}

.mobile-menu .close-btn {
  position: absolute;
  top: 1rem;
  right: 1rem;
  font-size: 1.8rem;
  background: none;
  border: none;
  color: var(--icon-color);
  cursor: pointer;
  transition: color var(--transition-time);
}
.mobile-menu .close-btn:hover {
  color: var(--hover-color);
}

.mobile-menu-links {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-top: 2rem;
}

.mobile-menu-links a {
  color: var(--text-color);
  text-decoration: none;
  padding: 1rem;
  border-radius: 4px;
  transition: all var(--transition-time);
  display: flex;
  align-items: center;
  gap: 1rem;
}
.mobile-menu-links a:hover {
  background: rgba(0, 0, 0, 0.1);
}

/* Mensajes y recordatorios */
.message,
.reminder {
  text-align: center;
  padding: 2rem;
  margin: 2rem 0;
  border-radius: 10px;
  animation: fadeIn 1s ease-out;
}

.message {
  background-color: rgba(0, 123, 255, 0.1);
}
.reminder {
  background-color: rgba(40, 167, 69, 0.1);
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(-20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Grid layout */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 1.5rem;
}

.grid-item {
  background-color: rgba(51, 51, 51, 0.05);
  padding: 1.5rem;
  border-radius: 8px;
  transition: transform var(--transition-time);
}
.grid-item:hover {
  transform: translateY(-5px);
}

/* Footer */
footer {
  background: var(--footer-bg);
  background-size: 200% 200%;
  animation: gradient-animation 3s infinite alternate;
  color: var(--text-color);
  text-align: center;
  padding: 2rem;
  margin-top: auto;
  position: relative;
  border-top: 4px solid transparent;
  box-shadow: 0 -2px 15px rgba(0, 123, 255, 0.3);
  overflow: hidden;
}

footer::before {
  content: "";
  position: absolute;
  top: -2px;
  left: 50%;
  width: 100%;
  height: 4px;
  background-size: 400% 400%;
  animation: neon-border 5s infinite linear;
  transform: translateX(-50%);
}

@keyframes neon-border {
  0% {
    background-position: 0% 50%;
  }
  100% {
    background-position: 100% 50%;
  }
}

/* Iconos sociales */
.social-icons a {
  color: var(--text-color);
  font-size: 1.8rem;
  transition: transform 0.3s ease, text-shadow 0.3s ease;
  display: inline-block;
  margin: 0 10px;
  text-shadow: 0 0 5px rgba(255, 255, 255, 0.5);
}

.social-icons a:hover {
  transform: translateY(-5px);
  text-shadow: 0 0 10px #00c6ff, 0 0 20px #007bff;
}

/* Botones flotantes */
#dark-mode-toggle,
#back-to-top {
  position: fixed;
  right: 20px;
  background-color: var(--hover-color);
  color: var(--icon-color);
  width: 50px;
  height: 50px;
  border-radius: 50%;
  border: none;
  cursor: pointer;
  box-shadow: var(--shadow);
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: transform var(--transition-time);
}

#dark-mode-toggle {
  bottom: 20px;
}

#back-to-top {
  bottom: 80px;
  opacity: 0;
  visibility: hidden;
}
#back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

#dark-mode-toggle:hover,
#back-to-top:hover {
  transform: scale(1.1);
}

/* Responsive */
@media (max-width: 768px) {
  .nav-links {
    display: none;
  }
  .menu-icon {
    display: block;
  }
  .navbar {
    padding: 1rem;
  }
  .mobile-menu-links a {
    font-size: 1.1rem;
  }
  #dark-mode-toggle,
  #back-to-top {
    width: 45px;
    height: 45px;
  }
  /* En móvil se reubica el Dark Mode */
  #dark-mode-toggle {
    bottom: 80px;
  }
}