HTML

<div id="modal" class="modal">
    <button id="close-button" class="close-button" aria-label="close" tabindex="0">✕</button>
    <div>
        <h1>Notice</h1>
        Lorem ipsum dolor sit amet.
    </div>
</div>

CSS


        body {
    overscroll-behavior-y: none;
    font-family: system-ui;
    padding: 2em;
    background-color: #f4f4f4;
}
.modal {
    position: fixed;
    top: 50%;
    left: 50%;
    min-width: 66%;
    transform: translate(-50%, -50%);
    padding: 1em 2em 2em 2em;
    background-color: white;
    box-shadow: 0 0 15px rgba(0,0,0,0.2);
}
.close-button {
    background: transparent;
    border: none;
    padding: 1em;
    font-size: 1em;
    position: absolute;
    right: 0;
    top: 0;
    cursor: pointer;
}

JS


        document.getElementById("close-button").onclick = () => {
    document.getElementById("modal").style.display = "none";
}