I am testing so css (css-grid) and here is the code:

```
<!doctype html>
<html lang="en">
  <head>

    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">

    <title></title>

    <style>

      html, body {
        height: 100%;
      }

      .container {
        display: grid;
        height:100%;
        grid-template-rows: 1fr 1fr 1fr;
        grid-template-columns: 1fr;
        grid-template-areas:
        "h h";
      }

      .header {
        height: 300px;
        grid-area: h;
        background-color: red;
      }

      .box {
        display: grid;
        background-color: green;
        height: 50px;
        width: 50px;
        align-self: center;
      }

    </style>

  </head>
  <body>

    <div class="container">
      <div class="header">
        <div class="box">Box1</div>
      </div>
    </div>

  </body>
</html>

```

If you look at class name 'box' above, you can see that it's got display: grid and align-self: center.

When I run this I'm getting this error in the console:

**"align-self has no effect on this element since it’s not a grid or flex item.
Try adding display:grid, display:flex, display:inline-grid, or display:inline-flex."**

As you can see display: grid is there...Why is this happening?