div#left_menu {
  position: fixed;
  margin-top: 10px;
  z-index: 100;
  border: 1px solid #e7e7e7;
}
div#left_menu > div#menu_button {
  position: absolute;
  top: 0px;
  right: -20px;
  height: 100px;
  width: 20px;
  cursor: ew-resize;
  writing-mode: vertical-rl; /* 세로로 글자를 출력 */
  text-orientation: upright; /* 글자가 직립되도록 설정 */
  border-radius: 0px 5px 5px 0px;
  border: 1px solid silver;
  background-color: #eaeaea;
}
div#left_menu > div.accordion {
  /* display:none; */
  background-color: white;
  width: 20px;
  display: none;
}
div#left_menu > div.accordion > div.accordion-item:hover {
  background-color: #e7e7e7;
}
div#left_menu > div.accordion > div.accordion-item > a {
  padding-left: 10px;
}
div#left_menu > div.accordion > div.accordion-collapse > a {
  padding-left: 30px;
}