如何将垂直滚动设置为主体上的模式弹出窗口

我正在尝试滚动到模式弹出窗口。在我打开模态弹出窗口后,如果按f12键检查元素,我想垂直滚动到模态弹出窗口。如果我移动垂直滚动弹出窗口,只移动。。如何在css中实现它? http://jsfiddle.net/sdjf48be/2/

css:

/* The Modal (background) */
.modal {
display: none; /* Hidden by default */
position: fixed; /* Stay in place */
z-index: 1; /* Sit on top */
padding-top: 100px; /* Location of the box */
left: 0;
top: 0;
width: 100%; /* Full width */
height: 100%; /* Full height */
overflow: auto; /* Enable scroll if needed */
background-color: rgb(0,0,0); /* Fallback color */
background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
}

/* Modal Content */
.modal-content {
background-color: #fefefe;
margin: auto;
padding: 20px;
border: 1px solid #888;
width: 80%;
}