How to do floating of labels in CSS
<p>I want to display the label of an input inside its input, so that when I click the input, the label will animate and go above the input and change the styles of the input's border.</p>

<p>Like so:</p>

<p><a href="https://i.stack.imgur.com/L29q0.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/L29q0.jpg" alt="Enter image description here"></a></p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-css lang-css prettyprint-override"><code>* {
  margin: 0;
  padding: 0;
}

form {
  width: 100%;
  max-width: 500px;
  margin: 0 auto;
  outline: 1px solid lightgrey;
  padding: 10px;
}

label, input[type='text'], input[type='password'] {
  font-size: 12pt;
  padding: 8px;
}

label {
  color: grey;
}

input {
  border: none;
  outline: none;
  border-bottom: 1px solid grey;
}</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;form&gt;
  &lt;label for="username"&gt;Username&lt;/label&gt;
  &lt;input id="username" name="username" type="text"/&gt;
  &lt;br/&gt;

  &lt;label for="password"&gt;Password&lt;/label&gt;
  &lt;input id="password" name="password" type="password"/&gt;
  &lt;br/&gt;

  &lt;input type="submit" value"login"/&gt;
&lt;/form&gt;</code></pre>
</div>
</div>
</p>

<p>How can I achieve this with CSS?</p>