:root {
  --color-bg: #f9f9f9;
  --color-primary: #2c3e50;
  --color-accent: #3498db;
  --color-text: #333;
  --color-link: #2c3e50;
  --color-white: #ffffff;
  --color-muted: #666;

  --font-main: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;

  --border-radius: 8px;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
}

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

body {
  font-family: var(--font-main);
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  padding: 1rem;
}

header {
  background-color: var(--color-primary);
  color: var(--color-white);
  text-align: center;
  padding: 2rem 1rem;
  margin-bottom: 2rem;
  border-radius: var(--border-radius);
}

header h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

header p {
  color: var(--color-accent);
  font-size: 1rem;
}

main {
  max-width: 1000px;
  margin: 0 auto;
  padding: 1rem;
}

h2 {
  font-size: 1.25rem;
  color: var(--color-primary);
  margin-bottom: 0.75rem;
}

p {
  margin-bottom: 1rem;
  color: var(--color-text);
}

ul {
  margin-bottom: 1rem;
  padding-left: 1rem;
}

ul li {
  margin-bottom: 0.5rem;
  list-style: disc;
  color: var(--color-muted);
}

code {
  background-color: #eaeaea;
  padding: 2px 5px;
  border-radius: 4px;
  font-family: monospace;
  font-size: 0.95em;
}

/* Lista de ejercicios */
.ejercicios {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2rem;
}

.ejercicio {
  background-color: var(--color-white);
  border-radius: var(--border-radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  transition: transform 0.2s ease;
}

.ejercicio:hover {
  transform: translateY(-3px);
}

.ejercicio a {
  display: inline-block;
  margin-top: 0.5rem;
  padding: 0.5rem 1rem;
  background-color: var(--color-accent);
  color: var(--color-white);
  text-decoration: none;
  border-radius: var(--border-radius);
  font-weight: bold;
  transition: background-color 0.2s ease;
}

.ejercicio a:hover {
  background-color: #217ab8;
}

/* Responsive grid para ejercicios */
@media (min-width: 640px) {
  .ejercicios {
    grid-template-columns: 1fr 1fr;
  }
}

@media (min-width: 960px) {
  .ejercicios {
    grid-template-columns: 1fr 1fr 1fr;
  }
}