*[id^='c']{
z-index: 3;
position: absolute;
}

#c0 {
z-index: 2;
position: absolute;
}





@media all and (min-width: 600px) {
  .aside { flex: 1 auto; }
}

@media all and (min-width: 800px) {
  .main    { flex: 3 0px; }
  .aside-1 { order: 1; } 
  .main    { order: 2; }
  .aside-2 { order: 3; }
  .footer  { order: 4; }
}

body {
  padding: 2em; 
}

.wrapper {
  display: flex;  
  flex-flow: row wrap;
  text-align: center;
}

.wrapper > * {
  padding: 10px;
  flex: 1 100%;
}