#page {
  max-width: 600px;
  margin: 0 auto;
}

#header {
  background: aqua;
  height: 70px;
  width: 550px;
  display: flex;
  /*flex-flow: row wrap;*/
  align-items: center;
  position: fixed;
  top: 0;
  padding-left: 50px;
  margin: 0px auto;
}

button {
  background-color: white;
  width: 80px;
  height: 30px;
}

#middle {
  margin-top: 70px;
  display: flex;
  justify-content: center;
}

#aside {
  background-color: orange;
  height: 500px;
  flex-grow: 1;
}

.main {
  background-color: red;
  height: 500px;
  flex-grow: 5;
  margin-left: 20px;
  margin-right: 20px;
}

.main #black {
  background-color: black;
  width: 50px;
  height: 50px;  
  position: relative;
  top: 440px;
  left: 350px;
}

#bside {
  background-color: purple;
  height: 500px;
  flex-grow: 1;
}

#footer {
  background-color: blue;
  width: 600px;
  height: 90px;
}