header {
  background-color: purple;
  height: 50px;
  display: flex;
  gap: 10px;
  align-items: center;
}

main {
  background: yellow;
  height: 500px;
  flex-grow: 3;
}

aside {
  background: lime;
  height: 500px;
  flex-grow: 1;
}

.item {
  background: cyan;
  width: 80px;
  height: 30px;
  margin-right: 10px;
}

div {
  display: flex;
  height: 500px;
}