div{
  border-radius: 5px;
}
.conteneur-flexible{
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100px;
  border: 2px solid purple;
  margin-bottom: 20px;
  background-color: 
  RGBa(120,0,240,0.1)
}
.element-flexible{
  width: 50px;
  height: 50px;
  background-color: #0AD;
  margin: 10px;
}