._sidebar {
position: absolute;
z-index: 2;
top: 3rem;
bottom: 0;
right: 0;
margin-top: 1px;
overflow-x: hidden;
overflow-y: scroll;
background: #f9f9f9;
background-image: initial;
background-position-x: initial;
background-position-y: initial;
background-size: initial;
background-repeat-x: initial;
background-repeat-y: initial;
background-attachment: initial;
background-origin: initial;
background-clip: content-box;
background-color: rgb(249, 249, 249);
background-clip: content-box;
-webkit-overflow-scrolling: touch;
-ms-overflow-style: none;
}
section {
outline: 0;
width: 300px;
outline-color: initial;
outline-style: initial;
outline-width: 0px;
}
aside,
section,
div {
display: block;
}
body {
height: 50%;
margin: 0;
overflow: auto;
font: normal 1em/1.7 "Open Sans", Helvetica, Arial, sans-serif;
font-style: normal;
font-variant: normal;
font-weight: normal;
font-stretch: normal;
font-size: 1em;
line-height: 1.7;
font-family: 'Open Sans', Helvetica, Arial, sans-serif;
color: #333;
word-wrap: break-word;
overflow-wrap: break-word;
-webkit-tap-highlight-color: transparent;
-webkit-touch-callout: none;
-webkit-text-size-adjust: 100%;
-ms-text-size-adjust: 100%;
}
._sidebar::-webkit-scrollbar {
-webkit-appearance: none;
background-color: rgb(255, 255, 255);
width: 10px;
}
._sidebar::-webkit-scrollbar-button {
display: none;
}
._sidebar::-webkit-scrollbar-thumb {
min-height: 2rem;
background: #d2d2d2;
background-image: initial;
background-position-x: initial;
background-position-y: initial;
background-size: initial;
background-repeat-x: initial;
background-repeat-y: initial;
background-attachment: initial;
background-origin: initial;
background-clip: padding-box;
background-color: rgb(210, 210, 210);
background-clip: padding-box;
border: 3px solid #fff;
border-top-color: rgb(255, 255, 255);
border-top-style: solid;
border-top-width: 3px;
border-right-color: rgb(255, 255, 255);
border-right-style: solid;
border-right-width: 3px;
border-bottom-color: rgb(255, 255, 255);
border-bottom-style: solid;
border-bottom-width: 3px;
border-left-color: rgb(255, 255, 255);
border-left-style: solid;
border-left-width: 2px;
border-radius: 5px;
border-top-left-radius: 5px;
border-top-right-radius: 5px;
border-bottom-right-radius: 5px;
border-bottom-left-radius: 5px;
}
._list {
margin: 0;
padding: 0;
list-style: none;
width: 18rem;
box-shadow: inset -1px 0 #e3e3e3;
}
<section class="_sidebar">
<div role="navigation" class="_list">
<a href="#">link1</a>
<br>
<a href="#">link1</a>
<br>
<a href="#">link1</a>
<br>
<a href="#">link1</a>
<br>
<a href="#">link1</a>
<br>
<a href="#">link1</a>
<br>
<a href="#">link1</a>
<br>
<a href="#">link1</a>
</div>
</section>