In the style.css it should be located around line 2219 –
.home hr {
border: none;
border-top: 1px solid #fff;
display: block;
height: 1px;
margin: 20px auto 30px;
width: 120px;
}
If you’ve made changes to your css file then it may be on a different line.
If you’re unable to find it, just send me a link to your site and I can find out where it’s located.