.login_form {
    width: 100%;
    max-width: 600px;
    margin: 40px auto;
    background: #000000;  /* 666666 or 888888 */
    color: #fff;
    padding: 20px 10px;
    border-radius: 8px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.5);
}