How does "#" (hash mark, number sign) close a modal box?

Question

I recently read this article about creating a pure CSS modal box:

• Creating a modal window with HTML5 & CSS3

I've tested the code and it works great. I'm using it for my site's contact and register/log-in pages.

There is one part of the code I haven't fully grasped.

How does this...

<a href="#close" title="Close" class="close">X</a>

...close the box?

There is nothing in the CSS that hides or removes an element with a close class, nor any similar function targeting href, #close or title. It's simply that one line of code by itself, and when the use clicks on it, the modal window closes (neatly and elegantly, I might add).

It's clear that the "close" text doesn't matter. The text could be anything and the function works. But if "#" is removed, the styling fails, but the window still closes.

So what's so special about "#"?

.modalDialog {
  position: fixed;
  font-family: Arial, Helvetica, sans-serif;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background: rgba(0, 0, 0, 0.8);
  z-index: 99999;
  opacity: 0;
  transition: opacity 400ms ease-in;
  pointer-events: none;
}
.modalDialog:target {
  opacity: 1;
  pointer-events: auto;
}
.modalDialog > div {
  width: 400px;
  position: relative;
  margin: 10% auto;
  padding: 5px 20px 13px 20px;
  border-radius: 10px;
  background: #fff;
}
.close {
  background: #606061;
  color: #FFFFFF;
  line-height: 25px;
  position: absolute;
  right: -12px;
  text-align: center;
  top: -10px;
  width: 24px;
  text-decoration: none;
  font-weight: bold;
  border-radius: 12px;
  box-shadow: 1px 1px 3px #000;
}
.close:hover {
  background: #00d9ff;
}

<a href="#openModal">Open Modal</a>

<div id="openModal" class="modalDialog">
  <div>
    <a href="#" title="Close" class="close">X</a>
    <h2>Modal Box</h2>
    <p>This is a sample modal box that can be created using the powers of CSS3.</p>
    <p>You could do a lot of things here like have a pop-up ad that shows when your website loads, or create a login/register form for users.</p>
  </div>
</div>

Answer 1

When you click on href="#openModal", it finds the fragment with id="openModal" and puts the focus on it. Changing its state. The css .modalDialog:target comes into action making the modal visible with opacity:1.

When you click on href="#close", it tries to find fragment id="close", which is not present. It also removes focus from any other fragment, making modalDialog loose focus. So nothing remains in focus. and modal closes.