SOURCE

<div class="box-wrapper">
  <div class="box">
    <div class="item">Home <span class="caret"></span></div>
    <div class="item">Phthon</div>
    <div class="item">React</div>
    <div class="item">Vue <span class="caret"></span></div>
    <div class="item">Java</div>
    <div class="item">Html5</div>
    <div class="item">Javascript</div>
    <div class="item">VuePress</div>
    <div class="item">Bootstrap</div>
    <div class="item">Jquery</div>
    <div class="item">Home</div>
    <div class="item">Order</div>
    <div class="item">Session</div>
    <div class="item">Preety</div>
    <div class="item">Java</div>
    <div class="item">Html5</div>
    <div class="item">Javascript</div>
    <div class="item">VuePress</div>
    <div class="item">Bootstrap</div>
    <div class="item">Jquery</div>
  </div>
</div>

.box-wrapper {
  width: 100px;
  background: #009688;
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  overflow: hidden;
  box-shadow: 0 0 10px 0 rgba(0, 0, 0, .8);
  height: 300px;
}
.box {
  height: 100%;
  width: calc(100% + 17px);
  overflow-y: auto;
  text-align: center;
  color: #f2f2f2;
}
.box .item {
  height: 40px;
  line-height: 40px;
  cursor: pointer;
  position: relative;
  
}