title: Why do I cannot center elements if i scale them
body: <p>I am using this to center things in CSS:</p>
  <pre><code>.testclass {
  display: flex;
  justify-content: center;
  }
  </code></pre>
  <p>but when i want to scale elements using <code>width</code> and <code>height</code>, it doesn't work and my elements are not centered.</p>
  <p>Like this:</p>
  <pre><code>.testclass {
  display: flex;
  justify-content: center;
  width: 200px;
  height: 200px;
  }
  </code></pre>
  <p>What's the problem?</p>