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CSS

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HTML 

              
                <h1>Default Tables are Weird</h1>

<table>
  <tr>
    <td>I'm a table</td>
    <td>and stuff</td>
  </tr>
</table>

<table>
  <tr>
    <td>I'm as wide</td>
    <td>as the cells are</td>
  </tr>
</table>

<table>
  <tr>
    <td>I can easily become 100% wide.</td>
    <td>and I'll stop there if I possibly can.</td>
  </tr>
</table>

<table>
  <tr>
    <td>If you don't specify it,</td>
    <td>the cells will be kind of arbitrarily wide depending on the content inside. This one is way wider right? ¯\(°_o)/¯</td>
  </tr>
</table>

<table class="respect">
  <tr>
    <td>If you <strong>do</strong> specify it,</td>
    <td>that will be respected if it's possible to do so. These should be 50% wide.</td>
  </tr>
</table>

<table class="thousand">
  <tr>
    <td>But things can get weird.</td>
    <td>I told both of these cells to be 1000px wide and it's like NOPE.</td>
  </tr>
</table>

<table class="calc">
  <tr>
    <td>It's kinda like a calculation. I'm told to be 2000px wide, thus I'm 66.66% wide (2/3 of total 3000px). </td>
    <td>And I'm told to be 1000px wide, thus I'm 33.33% wide (1/3 of total 3000px).</td>
  </tr>
</table>

<table class="image">
  <tr>
    <td>An image that's too wide though?</td>
    <td>That'll bust out like nobody's business.
    <img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/3/dock-slice-2.png" />
    You can try hiding the overflow but that doesn't work.
    </td>
  </tr>
</table>
  
<table class="whitespace">
  <tr>
    <td>Or some non-wrapping text?</td>
    <td>That'll blast out a table in short order like this.</td>
  </tr>
</table>
  
<table class="code">
  <tr>
    <td>Which is an issue for preformatted text, like code.</td>
    <td><pre>
body.logged-in article > h2 {
  background: linear-gradient(rgba(0, 0, 0, 0), rgba(255, 0, 0, 0.2));      
}
    </pre></td>
  </tr>
</table>
!

CSS 

              
                td {
  border: 1px solid black;
}
table {
  margin: 15px 0;
  border: 1px solid black;
}
html {
  background: #ccc;
}
body {
  max-width: 400px;
  margin: 0 auto;
  background: white;
  padding: 10px;
}

.respect td {
  width: 50%;
}

.thousand td {
  width: 1000px;
}

.image td {
  overflow: hidden;
}

.whitespace td {
  white-space: nowrap;
}

.calc td:nth-child(1) {
  width: 2000px;
}
.calc td:nth-child(2) {
  width: 1000px;
}
!

JS
!
999px

Console