.dialog {

    width: calc(100% - 40px);
    max-width: 400px;
    border: none;
    inset: 0;

    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);

    box-shadow: 0 3px 10px -.5px rgba(0, 0, 0, .2);
    text-align: center;
    padding: 30px;
    border-radius: 3px;
    background-color: #222;
    transition: 0.3s all;
}
dialog[open] {
    display: block;
}
dialog::backdrop {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 1);
}