style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
header {
  text-align: center;
  width: 100%;
  background-color: darkblue;
  color: aliceblue;
  padding: 1rem;
  position: fixed;
  top: 0;
}
.container {
  margin-top: 60px;
}
/* aside */
aside {
  float: left;
  padding: 2rem;
}
a {
  text-decoration: none;
  font-size: 1.5rem;
  text-align: center;
}
aside li {
  list-style-type: none;
  padding: 15px 25px;
  margin: 3px;
  background-color: antiquewhite;
  border-radius: 20px;
}

/* main */
.main__pages {
  /* float: right; */
  padding: 2rem;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  gap: 2rem 2rem;
}
.page {
  box-shadow: 2px 2px 2px 2px rgba(0, 0, 0, 0.5);
}
img {
  max-width: 100%;
  height: auto;
}

@media (max-width: 1024px) {
  html {
    font-size: 13px;
  }
  .main__pages {
    grid-template-columns: repeat(2, 1fr);
  }
}
@media (max-width: 768px) {
  .main__pages {
    grid-template-columns: 1fr;
  }
  aside {
    float: none;
    padding: 1rem 1rem 0;
  }
  aside ul {
    display: flex;
    justify-content: space-between;
  }
  aside li {
    display: inline-block;
  }
}
@media (max-width: 406px) {
  h1 {
    font-size: 1.5rem;
  }
}