* {
  box-sizing: border-box;
}
.header {
  border: 1px solid red;
  padding: 15px;
}
.menu {
  width: 25%;
  float: left;
}
.main {
  width: 75%;
  float: left;
  background-image: url("../pics/jpeg/soliton_clouds_bd.jpg");
}