body {
  background-color: #f5f5f5;
  font-family: sans-serif;
  margin: 0;
}

.container {
  display: grid;
  grid-template-areas:
    "header"
    "nav"
    "main";
  grid-template-rows: auto 1fr;
  height: 100vh;
}

.header {
  grid-area: header;
  padding: 1rem;
}

.header h1 {
  margin: 0;
}

.subtitle {
  font-size: 0.8em;
  color: #666;
  margin-top: 0.5rem;
}

.separator {
  border-bottom: 1px solid #ccc;
  margin: 1rem 0;
}

.nav {
  grid-area: nav;
  overflow-y: auto;
  padding: 1rem;
  border-right: 1px solid #ccc;
}

.main {
  grid-area: main;
  overflow-y: auto;
  padding: 1rem;
}

@media (min-width: 768px) {
  .container {
    grid-template-areas:
      "header header"
      "nav main";
    grid-template-columns: 1fr 5fr;
  }
}