<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" content="width=device-width, height=device-height" />
    <title>Color Grid</title>
  </head>
  <style>
    body {
      margin: 0;
    }
    .container {
      display: grid;
      grid-template-columns: 1fr 1fr 1fr;
    }
    .box {
      height: 100vh;
      width: 33.33vw;
    }
    .red {
      background-color: rgb(255, 0, 0);
      color-adjust: exact;
    }
    .green {
      background-color: rgb(0, 255, 0);
      color-adjust: exact;
    }
    .blue {
      background-color: rgb(0, 0, 255);
      color-adjust: exact;
    }
  </style>

  <body>
    <div class="container">
      <div class="red box"></div>
      <div class="green box"></div>
      <div class="blue box"></div>
    </div>
  </body>
</html>
