Modal windows are an interactive element of a webpage that overlays the main content and requires user interaction. Typically, they are implemented using JavaScript to provide dynamic behavior. However, it is possible to create a basic modal window using only CSS. This article outlines the steps to achieve this goal.

1. Basic HTML Structure

The first step is to create a basic HTML structure for the modal window. This includes defining a container for the modal window and a button to activate it.

<div id="modal" class="modal">
    <div class="modal-content">
        <span class="close">&times;</span>
        <p>This is a modal window.</p>
    </div>
</div>

<button id="modalBtn">Open Modal Window</button>

2. Styling the Modal Window Using CSS

Now, let's style the modal window using CSS. We'll need to hide the modal window until it's activated and then display it above the page content with a semi-transparent background.

.modal {
    display: none; 
    position: fixed; 
    z-index: 1; 
    left: 0;
    top: 0;
    width: 100%; 
    height: 100%; 
    overflow: auto; 
    background-color: rgba(0,0,0,0.4); 
}

.modal-content {
    background-color: #fefefe;
    margin: 15% auto; 
    padding: 20px;
    border: 1px solid #888;
    width: 80%; 
}

.close {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: black;
    text-decoration: none;
    cursor: pointer;
}

3. Utilizing CSS to Show and Hide the Modal Window

To show and hide the modal window, we'll use the :target pseudo-class. This technique allows us to change the styles of an element that is the target of the current URL. Therefore, clicking the button will change the URL fragment, activating the modal window.

#modal:target {
    display: block;
}

4. Implementing the Closing Mechanism

To close the modal window, we'll use a link that changes the URL fragment back to a non-existent element. We'll add a close button to the modal window that links back to the page.

<a href="#" class="close">&times;</a>

Using the above steps, it's possible to create a basic modal window using only HTML and CSS. This method provides a simple way to implement modal windows without requiring JavaScript. However, for more complex interactions and dynamic content changes within the modal window, it's advisable to consider using JavaScript.