lopyx

<div class="message-wrapper">
    <div class="message">
        <h2>Test</h2>
    </div>
</div>

.message-wrapper {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: rgba(0, 0, 0, 0.3);
    z-index: 1;
}
.message {
    background-color: #ffffff;
}