/* Small devices (portrait tablets and large phones, 600px and up) */
@media only screen and (min-width: 320px){
  .yellow {
    background-color: yellow;
  }

  .blue {
    background-color: blue;
  }

  .red {
    background-color: red;
  }

  .green {
    background-color: green;
  }

  .pink {
    background-color: pink;
  }

  .purple {
    background-color: purple;
  }

  .main-container {
    display: flex;
    flex-flow: column wrap;
    justify-content: center;
    align-items: center;
  }

  .item {
    width: 100%;
    height: 100px;
  }
}

/* Medium devices (landscape tablets, 768px and up) */
@media only screen and (min-width: 768px) {
  .main-container{
    flex-flow: row wrap;
  }

  .item{
    width: 50%;
  }
}

/* Large devices (laptops/desktops, 992px and up) */
@media only screen and (min-width: 992px) {
  .item{
    width: 33.3%;
  }
}

/* Extra large devices (large laptops and desktops, 1200px and up) */
@media only screen and (min-width: 1200px) {
  .main-container{
    justify-content: flex-start;
  }

  .item{
  width: 25%;
}