body{
  margin:0;
  font-family:Arial;
  background:#eee;
}

.container{
  display:grid;
  grid-template-columns:150px auto;
  grid-template-rows:50px auto;
  height:100vh;
}

.header{
  grid-column:1/3;
  background:#444;
  color:#fff;
  padding:10px;
}

.sidebar{
  background:#222;
  color:white;
  padding:10px;
}

.main{
  padding:10px;
  display:grid;
  grid-template-columns:repeat(2,1fr);
  gap:10px;
}

.box{
  background:white;
  padding:15px;
  text-align:center;
}

.dark{
  background:#111;
  color:white;
}

.dark .header,
.dark .sidebar{
  background:black;
}

.dark .box{
  background:#333;
}