CSS Grid Layout not working in IE11 even with prefixes

I'm using following HTML markup for my grid.

<section class="grid">
    <article class="grid-item width-2x height-2x">....</article>
    <article class="grid-item">....</article>
    <article class="grid-item">....</article>
    <article class="grid-item width-2x">....</article>
    <article class="grid-item height-2x">....</article>
    <article class="grid-item">....</article>
    <article class="grid-item">....</article>
    <article class="grid-item width-2x height-2x">....</article>
</section>

The SCSS code is something like below:

.grid {
    display: grid;
    grid-template-columns: repeat( 4, 1fr );
    grid-gap: 30px;
    align-items: start;

    .grid-item {
        &.height-2x {
            grid-row: span 2;
        }
        &.width-2x {
            grid-column: span 2;
        }
    }
}

Since I'm using auto-prefixer in my workflow it automatically adds all relevant properties with -ms prefix. I can confirm it via inspect element.

Now, the issue is this code works just fine in Chrome, Firefox and Opera, but when I open this page in Microsoft Edge or in IE 11 all grid items are overlapping each other at first cell. According to this site these browsers support CSS Grid layout with -ms prefix. I've created a CodePen for this scenario.

CodePen Link

Why is it not working?

.grid {
  display: -ms-grid;
  display: grid;
  -ms-grid-columns: (1fr)[4];
  grid-template-columns: repeat(4, 1fr);
  -ms-grid-rows: (270px)[4];
  grid-template-rows: repeat(4, 270px);
  grid-gap: 30px;
}

.grid .grid-item {
  background-color: #000;
  color: #fff;
  text-align: center;
  line-height: 270px;
}

.grid .grid-item.height-2x {
  -ms-grid-row: span 2;
  grid-row: span 2;
}

.grid .grid-item.width-2x {
  -ms-grid-column: span 2;
  grid-column: span 2;
}

<section class="grid">
  <article class="grid-item width-2x height-2x">....</article>
  <article class="grid-item">....</article>
  <article class="grid-item">....</article>
  <article class="grid-item width-2x">....</article>
  <article class="grid-item height-2x">....</article>
  <article class="grid-item">....</article>
  <article class="grid-item">....</article>
  <article class="grid-item width-2x height-2x">....</article>
</section>