dd.css

.dropup,
.dropright,
.dropdown,
.dropleft {
  position: relative;
}

.dropdown-toggle::after {
  display: inline-block;
  width: 0;
  height: 0;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0.3em solid;
  border-right: 0.3em solid transparent;
  border-bottom: 0;
  border-left: 0.3em solid transparent;
}

.dropdown-toggle:empty::after {
  margin-left: 0;
}

.dropdown-menu {
  position: absolute;
  top: 100%;
  left: 0;
  z-index: 1000;
  display: none;
  float: left;
  min-width: 10rem;
  padding: 0.5rem 0;
  margin: 0.125rem 0 0;
  font-size: 1rem;
  color: #212529;
  text-align: left;
  list-style: none;
  background-color: #fff;
  background-clip: padding-box;
  border: 1px solid rgba(0, 0, 0);
}

.dropdown-menu-right {
  right: 0;
  left: auto;
}

.dropup .dropdown-menu {
  top: auto;
  bottom: 100%;
  margin-top: 0;
  margin-bottom: 0.125rem;
}

.dropup .dropdown-toggle::after {
  display: inline-block;
  width: 0;
  height: 0;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0;
  border-right: 0.3em solid transparent;
  border-bottom: 0.3em solid;
  border-left: 0.3em solid transparent;
}

.dropup .dropdown-toggle:empty::after {
  margin-left: 0;
}

.dropright .dropdown-menu {
  top: 0;
  right: auto;
  left: 100%;
  margin-top: 0;
  margin-left: 0.125rem;
}

.dropright .dropdown-toggle::after {
  display: inline-block;
  width: 0;
  height: 0;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0.3em solid transparent;
  border-right: 0;
  border-bottom: 0.3em solid transparent;
  border-left: 0.3em solid;
}

.dropright .dropdown-toggle:empty::after {
  margin-left: 0;
}

.dropright .dropdown-toggle::after {
  vertical-align: 0;
}

.dropleft .dropdown-menu {
  top: 0;
  right: 100%;
  left: auto;
  margin-top: 0;
  margin-right: 0.125rem;
}

.dropleft .dropdown-toggle::after {
  display: inline-block;
  width: 0;
  height: 0;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
}

.dropleft .dropdown-toggle::after {
  display: none;
}

.dropleft .dropdown-toggle::before {
  display: inline-block;
  width: 0;
  height: 0;
  margin-right: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0.3em solid transparent;
  border-right: 0.3em solid;
  border-bottom: 0.3em solid transparent;
}

.dropleft .dropdown-toggle:empty::after {
  margin-left: 0;
}

.dropleft .dropdown-toggle::before {
  vertical-align: 0;
}

.dropdown-menu[x-placement^="top"], .dropdown-menu[x-placement^="right"], .dropdown-menu[x-placement^="bottom"], .dropdown-menu[x-placement^="left"] {
  right: auto;
  bottom: auto;
}

.dropdown-divider {
  height: 0;
  margin: 0.5rem 0;
  overflow: hidden;
  border-top: 1px solid #e9ecef;
}

.dropdown-item {
  display: block;
  padding: 0.25rem 1.5rem;
  clear: both;
  font-weight: 400;
  color: #212529;
  text-align: inherit;
  white-space: nowrap;
  background-color: transparent;
  border: 0;
}

.dropdown-item:hover, .dropdown-item:focus {
  color: #16181b;
  text-decoration: none;
  background-color: #9bc;
}

li.active, .dropdown-item.active, .dropdown-item:active {
  color: #fff;
  text-decoration: none;
  background-color: #9bc;
}

.dropdown-item.disabled, .dropdown-item:disabled {
  color: #6c757d;
  background-color: transparent;
}

.dropdown-menu.show {
  display: block;
}

.dropdown-header {
  display: block;
  padding: 0.5rem 1.5rem;
  margin-bottom: 0;
  font-size: 0.875rem;
  color: #6c757d;
  white-space: nowrap;
}

.dropdown-item-text {
  display: block;
  padding: 0.25rem 1.5rem;
  color: #212529;
}