How to style the scroll of a div

Question

hello, I’d like to know how I style the scrollbar of this div, and something else, when passing the name on the names the effect Hover it opens a div to the left, after I put in that div that holds the names overflow: auto doesn’t work the Hover effect of it that would show the other div, when I take the overflow: auto works normally, can anyone help me ? what am I doing wrong ? http://prntscr.com/ip0jju

#usuarios {
  position: relative;
  width: 200px;
  height: 364px;
  max-height: 364px;
  overflow: auto;
  border: 3px solid #c9c9c9;
}

 ::-webkit-scrollbar #usuarios {
  width: 10px;
}

 ::-webkit-scrollbar-button #usuarios {
  width: 10px;
}

 ::-webkit-scrollbar-track #usuarios {
  width: 10px;
}

 ::-webkit-scrollbar-track-piece#usuarios {
  width: 10px;
}

 ::-webkit-scrollbar-thumb #usuarios {
  width: 10px;
}

 ::-webkit-scrollbar-corner #usuarios {
  width: 10px;
}

 ::-webkit-resizer #usuarios ul li {
  position: relative;
}

#usuarios ul li:first-child {
  margin: 5px 0 0 0;
  font-weight: bold;
}

#usuarios ul li:last-child {
  margin: 0 0 5px 0;
}

#usuarios ul li a {
  display: block;
  margin: 0 5px;
  padding: 0 5px;
  height: 25px;
  line-height: 26px;
  font-weight: bold;
  font-size: 12px;
  text-transform: capitalize;
  color: #000;
}

#usuarios ul li .admin {
  margin: 0 5px 5px 5px;
  background-color: rgba(255, 255, 255, 0.8);
}

#usuarios ul li:hover .admin {
  border-radius: 10px;
}

#usuarios ul li:hover a {
  background-color: rgba(255, 255, 255, 0.8);
  -webkit-border-radius: 5px;
  -moz-border-radius: 5px;
  border-radius: 5px;
}

#usuarios ul li:hover a span {
  opacity: .95;
}

#usuarios ul li a span {
  display: block;
  margin: 4px 0 0 0;
  width: 18px;
  height: 18px;
  line-height: 19px;
  text-align: center;
  font-size: 7px;
  font-weight: bold;
  color: #fff;
  opacity: .60;
  border-radius: 50%;
}

#usuarios ul li .on {
  color: green;
}

#usuarios ul li .aus {
  color: orange;
}

#usuarios ul li .off {
  color: #ff0000;
}

#usuarios ul li a .on {
  color: #fff;
  background-color: green;
}

#usuarios ul li a .aus {
  color: #fff;
  background-color: orange;
}

#usuarios ul li a .off {
  color: #fff;
  background-color: #ff0000;
}

#usuarios ul li ul li .perfil {
  display: none;
}

#usuarios ul li:hover ul li .perfil {
  display: block;
  z-index: 9999;
  position: absolute;
  left: -215px;
  top: -35px;
  width: 200px;
}

#usuarios ul li:hover ul li .perfil .box_perfil {
  width: 196px;
  height: 200px;
  border: 3px solid #000;
  background-color: rgba(0, 0, 0, 0.5);
}

<div id="usuarios" class="usuarios align_right border-radius rgba">

  <ul>
    <li><a href="javascript:void(0)" class="on admin border-radius">Admin <span class="on align_right">ON</span></a>
      <ul>
        <li>
          <div class="perfil">
            <div class="box_perfil"></div>
          </div>
        </li>
      </ul>
    </li>
    <li><a href="javascript:void(0)" class="on">Amanda <span class="on align_right">ON</span></a></li>
    <li><a href="javascript:void(0)" class="on">Joana <span class="on align_right">ON</span></a></li>
    <li><a href="javascript:void(0)" class="on">Pedro <span class="on align_right">ON</span></a></li>
    <li><a href="javascript:void(0)" class="on">Bruna <span class="on align_right">ON</span></a></li>
    <li><a href="javascript:void(0)" class="on">Lohana <span class="on align_right">ON</span></a></li>
    <li><a href="javascript:void(0)" class="on">Julio <span class="on align_right">ON</span></a></li>
    <li><a href="javascript:void(0)" class="aus">Amanda <span class="aus align_right">AUS</span></a></li>
    <li><a href="javascript:void(0)" class="aus">Felipe <span class="aus align_right">AUS</span></a></li>
    <li><a href="javascript:void(0)" class="aus">Igor <span class="aus align_right">AUS</span></a></li>
    <li><a href="javascript:void(0)" class="off">Lucas <span class="off align_right">OFF</span></a></li>
    <li><a href="javascript:void(0)" class="off">Amanda <span class="off align_right">OFF</span></a></li>
    <li><a href="javascript:void(0)" class="off">Bruna <span class="off align_right">OFF</span></a></li>
    <li><a href="javascript:void(0)" class="off">Jéssica <span class="off align_right">OFF</span></a></li>
  </ul>
</div>