<main>
    <div></div>
    <div class=a2></div>
    <div></div>
    <div class=a4></div>
    <div class=a1></div>
    <div></div>
    <div class=a3></div>
    <div></div>
    <div class=a4></div>
    <div class=a1></div>
    <div></div>
    <div class=a2></div>
    <div></div>
    <div class=a4></div>
  </main>

index.html

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    height: 100vH;
  }

  body{
    display:grid;
    height: 100%;
    width: 100%;
    grid-template-columns: repeat(3 1fr);
    grid-template-rows: repeat (4 1fr);
    background-image: linear-gradient(to right, CornflowerBlue, SlateBlue);
  }

  main{
    display:grid;
    align-items: stretch;
  }
  div {
   height:35vH;
   background-image: linear-gradient(to right, DodgerBlue,Cornflowerblue,DodgerBlue);
  }
  .a1 {
   background-image: linear-gradient(CornflowerBlue, RoyalBlue,CornflowerBlue);
   grid-column-end: span 13;
  }
  .a2 {
   background-image: linear-gradient(to left, RoyalBlue,CornflowerBlue,RoyalBlue);
   grid-column-end: span 7;
  }
  .a3 {
   height: 35vH;
   background-image: radial-gradient(SlateBlue,CornflowerBlue);
   border-radius: 100px / 100px;
   grid-column-end: span 7;
  }
  .a4{
    height:35vH;
    background-image: radial-gradient(RoyalBlue,SlateBlue,CornflowerBlue);
     border-radius: 100px / 100px;
   grid-column-end: span 4;
  }

index.css