prevent body scroll on modal close - modal-dialog

Question

I have a simple html/css modal dialog that I close with a button and onclick event handlers in javascript. When the modal window is closed, the body of the site scrolls to the top of the screen. I need to prevent this.
Here is my code:
function modalClose() {
if (location.hash == '#log_in') {
location.hash = '';
}
}
// Handle ESC key (key code 27)
document.addEventListener('keyup', function(e) {
if (e.keyCode == 27) {
modalClose();
}
});
var modal = document.querySelector('#log_in');
// Handle click on the modal container
modal.addEventListener('click', modalClose, false);
// Prevent event bubbling if click occurred within modal content body
modal.children[0].addEventListener('click', function(e) {
e.stopPropagation();
}, false);
.modalDialog {
position: fixed;
font-family: Arial, Helvetica, sans-serif;
top: 0;
right: 0;
bottom: 0;
left: 0;
background: rgba(0, 0, 0, 0.8);
z-index: 99999;
opacity: 0;
-webkit-transition: opacity 400ms ease-in;
-moz-transition: opacity 400ms ease-in;
transition: opacity 400ms ease-in;
pointer-events: none;
}
.modalDialog:target {
opacity: 1;
pointer-events: auto;
}
.modalDialog > div {
height: auto;
width: 75%;
position: relative;
margin-top: 2%;
margin-bottom: 10%;
margin-left: 10%;
margin-right: 10%;
padding: 5px 20px 13px 20px;
border-radius: 10px;
background: #fff;
}
.close {
background: #606061;
color: #FFFFFF;
line-height: 25px;
position: absolute;
right: -11px;
text-align: center;
top: -10px;
width: 24px;
text-decoration: none;
font-weight: bold;
-webkit-border-radius: 12px;
-moz-border-radius: 12px;
border-radius: 12px;
-moz-box-shadow: 1px 1px 3px #000;
-webkit-box-shadow: 1px 1px 3px #000;
box-shadow: 1px 1px 3px #000;
text-indent: 0px;
}
.close:hover {
background: navy;
}
<link href="https://thomaswurdinger.com/Store_Reboot/css/styles.css" rel="stylesheet" />
<script src="https://thomaswurdinger.com/Store_Reboot/js/js.js"></script>
<link href="https://thomaswurdinger.com/Store_Reboot/css/style.css" rel="stylesheet" />
<div id="log_in" class="modalDialog">
<div>
X
<div>Modal Contents</div>
</div>
</div>

Answer 1

I changed :
if (location.hash == '#log_in') {
location.hash = '';
}
to:
if (location.hash == '#log_in') {
location.hash = 'pagename.php';
}