18F/calc

.timeout-dialog {
    position: fixed;
    top: 10%;
    left: 30%;
    width: 40%;
    padding: 16px;
    background: #fff;
    color: #333;
    z-index:2002;
    overflow: auto;
    text-align: center;
  }
  .session_security_overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: #000;
    z-index:1001;
    opacity:.75;
    -moz-opacity: 0.75;
    filter: alpha(opacity=75);
}

.session_security_modal {
    position: fixed;
    top: 25%;
    left: 25%;
    width: 50%;
    padding: 16px;
    background: #fff;
    color: #333;
    z-index:2002;
    overflow: auto;
    text-align: center;
}