title: Collapsing borders using CSS Grid
body: <p>I'm having fun getting my head around the new CSS Grid spec, but I'm running into trouble with borders.</p>
  <p><strong>Is it possible to collapse borders in a CSS Grid, or is there any way to style the gutter?</strong></p>
  <p>As you can see in the snippet below, the <code>10px</code> borders stack (<code>20px</code> total) in-between blocks.</p>
  <p>I understand this issue isn't unique to CSS Grids, but I'm hoping it'll allow for new solutions for creating a uniform 10px border between all boxes and on the outer edges.</p>
  <p>My actual use-case is a calendar I'm making to practice working with Grids and React components. You can see the issue I'm running into here:</p>
  <p><img src="https://i.stack.imgur.com/RrCX2.png" alt="CSS Grid Calendar" />.</p>
  <p>Since every month is different, I'll have a lot of different edge-cases to consider.</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.container {
    display: grid;
    grid-template-columns: 120px 120px;
    box-sizing: border-box;
  }
  
  .block {
    width: 100px;
    height: 100px;
    background-color: lightgrey;
    border: 10px solid palegreen;
  }
  
  .first {
    grid-column: 2 / span 1;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class='container'&gt;
    &lt;div class='block first'&gt;1&lt;/div&gt;
    &lt;div class='block'&gt;2&lt;/div&gt;
    &lt;div class='block'&gt;3&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>