* {
  box-sizing: border-box;
}

body {
  padding: 0;
}

#fbox {
  width: 60vw;
  height: 100vh;
  position: fixed;
  top: 0;
  left: 20%;
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-content: space-between;
  align-items: center;
  flex-wrap: wrap;
}

#headfoot {
  background-color: gray;
  width: 100%;
  height: 40px;
  display: flex;
  justify-content: center;
  align-items: center;
}

#sidebar {
  background-color: blue;
  height: calc(100vh - 80px);
  width: 20%;
  display: flex;
  justify-content: center;
  align-items: center;
}

#middle{
  background-color: green;
  flex-grow: 1;
  height: calc(100vh - 80px);
  display: flex;
  justify-content: center;
  align-items: center;
}