Fixed at side
HTML
<!-- Fixed at the middle of left side -->
<div class="fixed-at-side fixed-at-side--l">...</div>
<!-- Fixed at the middle of right side -->
<div class="fixed-at-side fixed-at-side--r">...</div>
CSS
.fixed-at-side {
position: fixed;
top: 50%;
transform: translate(0px, -50%);
}
.fixed-at-side--l {
left: 0;
}
.fixed-at-side--r {
right: 0;
}
Demo