Create a Centered Full-screen Overlay or Modal with CSS Grid

.overlay-container {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.6); /* Semi-transparent black background */
    backdrop-filter: blur(5px); /* Optional: blur background content */
    display: grid; /* Use Grid for centering */
    place-items: center; /* Centers content both horizontally and vertically */
    z-index: 1000; /* Ensure it's on top of other content */
    /* Optionally hide/show with visibility: hidden; opacity: 0; transition: all 0.3s; */
}

.modal-content {
    background-color: white;
    padding: 30px;
    border-radius: 8px;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
    max-width: 500px;
    text-align: center;
}

.close-button {
    margin-top: 20px;
    padding: 10px 20px;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}

<!-- HTML Structure -->
<button onclick="document.querySelector('.overlay-container').style.display = 'grid'">Open Modal</button>

<div class="overlay-container" style="display: none;">
    <div class="modal-content">
        <h2>Welcome to the Modal!</h2>
        <p>This is a perfectly centered modal window.</p>
        <button class="close-button" onclick="document.querySelector('.overlay-container').style.display = 'none'">Close</button>
    </div>
</div>