HTML

responsive sidebar menu css

<aside>
  <p> Menu </p>
  <a href="javascript:void(0)">
    <i class="fa fa-user-o" aria-hidden="true"></i>
    My drive
  </a>
  <a href="javascript:void(0)">
    <i class="fa fa-laptop" aria-hidden="true"></i>
    Computers
  </a>
  <a href="javascript:void(0)">
    <i class="fa fa-clone" aria-hidden="true"></i>
    Shared with me
  </a>
  <a href="javascript:void(0)">
    <i class="fa fa-star-o" aria-hidden="true"></i>
    Starred
  </a>
  <a href="javascript:void(0)">
    <i class="fa fa-trash-o" aria-hidden="true"></i>
    Trash
  </a>
</aside>
<style>
aside {
  color: #fff;
  width: 250px;
  padding-left: 20px;
  height: 100vh;
  background-image: linear-gradient(30deg , #0048bd, #44a7fd);
  border-top-right-radius: 80px;
}

aside a {
  font-size: 12px;
  color: #fff;
  display: block;
  padding: 12px;
  padding-left: 30px;
  text-decoration: none;
  -webkit-tap-highlight-color:transparent;
}

aside a:hover {
  color: #3f5efb;
  background: #fff;
  outline: none;
  position: relative;
  background-color: #fff;
  border-top-left-radius: 20px;
  border-bottom-left-radius: 20px;
}

aside a i {
  margin-right: 5px;
}

aside a:hover::after {
  content: "";
  position: absolute;
  background-color: transparent;
  bottom: 100%;
  right: 0;
  height: 35px;
  width: 35px;
  border-bottom-right-radius: 18px;
  box-shadow: 0 20px 0 0 #fff;
}

aside a:hover::before {
  content: "";
  position: absolute;
  background-color: transparent;
  top: 38px;
  right: 0;
  height: 35px;
  width: 35px;
  border-top-right-radius: 18px;
  box-shadow: 0 -20px 0 0 #fff;
}

aside p {
  margin: 0;
  padding: 40px 0;
}

body {
  font-family: 'Roboto';
  width: 100%;
  height: 100vh;
  margin: 0;
}
</style>