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

  :root {
    font: 1.2em/1.4 Arial, Helvetica, sans-serif;
  }

  body {
    padding: 0 0 1em;
  }

  header {
    background-color: #333;
    color: #fff;
    border: 5px solid #000;
  }

  header ul {
    list-style: none;
    margin: 0;
    padding: 0;
  }

  header a {
    color: #fff;
    text-decoration: none;
    display: block;
    padding: 0.5em 1em;
    border-top: 1px solid #999;
  }

  header .title {
    font-size: 150%;
    font-style: italic;
    font-weight: bold;
    padding: 1em;
  }

  main {
    padding: 0 1em;
  }

  .cards {
    list-style: none;
    margin: 0;
    padding: 0;
  }

  .cards li {
    border: 5px solid #000;
    margin-bottom: 1em;
  }

  .cards h2 {
    background-color: #333;
    color: #fff;
    margin: 0;
    padding: 0.5em 1em;
  }

  .cards .inner {
    padding: 0.5em 1em;
  }

  .sidebar {
    background-color: #333;
    border: 5px solid #000;
    padding: 0.5em 1em;
    color: #ffdf;
  }

  @media (min-width: 40em) {
    header {
      display: flex;
    }

    header nav ul {
      display: flex;
    }

    header nav {
      display: flex;
      margin-inline-start: auto;
      align-items: center;
    }

    header a {
      border-top: none;
    }

    main {
      display: flex;
      flex-direction: row;
    }

    .cards {
      display: flex;
      flex-direction: row;
      flex-wrap: wrap;
      gap: 1rem;
    }

    .cards li {
      flex-grow: 1;
      max-width: 19rem;
    }

  }