JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="left"></div>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">4</span> <span class="big-block">5</span> <span class="big-block">6</span>
    <span class="big-block">7</span> <span class="big-block">8</span> <span class="big-block">9</span>
    <span class="big-block">10</span> <span class="big-block">11</span> <span class="big-block">12</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
    <span class="big-block">1</span> <span class="big-block">2</span> <span class="big-block">3</span>
</div>

CSS

.main {
     width: 500px;
     height: 500px;
     background-color: blue;
}
.left {      
  -webkit-shape-outside: polygon(0 70px, 100% 70px, 100% 120px, 0 120px);
  float: left;
  width: 100%;
  height: 500px;
  background-color: lightgray;
  opacity:.8;
  -webkit-clip-path: polygon(0 70px, 100% 70px, 100% 120px, 0 120px);
}
.big-block {
   display: inline-block;
   width: 50px;
   height: 50px;
   background-color: red;
   font-size: 40px;
}