/* all */
* {
  outline: red 2px dotted;
}

body {
  background: blanchedalmond;
  padding: 0;
  margin: 0;
}
.container div {
  text-align: center;
  margin: 2%;
}
.container {
  height: 100vh;
  display: flex;
  flex-direction: column;
}

/* mobile */
.a {
  flex-grow: 1;
  width: 96%;
}
.b {
  flex-grow: 4;
  width: 96%;
}
.c {
  flex-grow: 1;
  width: 96%;
}

/* desktop */
@media (min-width: 600px) {
  .container {
    flex-direction: row;
    flex-wrap: wrap;
  }

  .a {
    width: 100%;
    height: 30%;
  }
  .b {
    width: 70%;
    height: 60%;
  }
  .c {
    width: 20%;
    height: 60%;
  }
}