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

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

  body {
    padding: 0;
    margin: 0;
  }

  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: #fff;
  }
  .container{
    max-width: 80rem;
    margin: 0 auto;
    padding-inline: 1rem;
  }

@media (min-width:40em){
  header{
    display: flex;
    justify-content: space-between;
    align-items: center;
    
    nav ul{
      display: flex;
    }
    nav a{
      border: 0;
    }
  }
  .cards{
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    
    li{
      flex: 0 1 calc(50% - 1rem);
    }
  }

  main{
    display: flex;
    gap: 1rem;
    margin-block-start: 1rem;
    flex-wrap: wrap;

    article{
      flex: 1 1 50rem;
    }

    aside{
      flex: 0 0 19rem;
    }

  }
}

@media (min-width:60em){
  .cards{

    li{
      flex: 0 1 calc(30% - 2rem);
    }
  }
}