metamask-extension/ui/app/css/itcss/components/simple-dropdown.scss

.simple-dropdown {
  height: 56px;
  display: flex;
  justify-content: flex-start;
  align-items: center;
  border: 1px solid $alto;
  border-radius: 4px;
  background-color: $white;
  font-size: 16px;
  color: #4d4d4d;
  cursor: pointer;
  position: relative;
}

.simple-dropdown__caret {
  color: $silver;
  padding: 0 10px;
}

.simple-dropdown__selected {
  flex-grow: 1;
  padding: 0 15px;
}

.simple-dropdown__options {
  z-index: 1050;
  position: absolute;
  height: 220px;
  width: 100%;
  border: 1px solid #d2d8dd;
  border-radius: 4px;
  background-color: #fff;
  -webkit-box-shadow: 0 3px 6px 0 rgba(0, 0, 0, .11);
  box-shadow: 0 3px 6px 0 rgba(0, 0, 0, .11);
  margin-top: 10px;
  overflow-y: scroll;
  left: 0;
  top: 100%;
}

.simple-dropdown__option {
  padding: 10px;

  &:hover {
    background-color: $gallery;
  }
}

.simple-dropdown__option--selected {
  background-color: $alto;

  &:hover {
    background-color: $alto;
    cursor: default;
  }
}

.simple-dropdown__close-area {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 1000;
  width: 100%;
  height: 100%;
}