html, body {
    display: flex;
    align-items: center;
    justify-content: center;
}
.cen {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 100%;
    height: 100%;
    
}
.allow {
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction:column;
    height: 400px;
    width: 400px;
    background-color: black;
    color: yellow;
    border: 30px outset red;
    border-radius: 20px;
    font-size: 20px;
    font-weight: bold;
    padding: 20px;
    margin-top: 10%;
}