php-flarum/ember/app/styles/flarum/dropdowns.less

.dropdown-menu {
  border: 0;
  padding: 8px 0;
  margin-top: 7px;
  background: @fl-body-bg;
  .box-shadow(0 2px 6px @fl-shadow-color);

  & > li > a {
    padding: 8px 15px;
    color: @fl-body-color;
    &:hover, &:focus {
      color: @fl-body-color;
      background-color: @fl-body-control-bg;
    }
    & .fa {
      margin-right: 5px;
      font-size: 14px;
    }
  }
  & .divider {
    margin: 10px 0;
    background-color: @fl-body-control-bg;
  }
}
.dropdown-split.item-count-1 {
  & .btn {
    border-radius: @border-radius-base !important;
  }
  & .dropdown-toggle {
    display: none;
  }
}

// PHONES
@media (max-width: @screen-xs-max) {
  .dropdown-open {
    overflow: hidden;
  }
  .dropdown-menu {
    margin: 0;
    position: fixed;
    left: 0 !important;
    right: 0 !important;
    width: auto !important;
    bottom: -100vh;
    top: auto;
    padding: 0;
    z-index: @zindex-modal;
    display: block;
    max-height: 100vh;
    border-radius: 0;
    .box-shadow(none);
    .transition(bottom 0.3s);

    &:before {
      content: " ";
      position: absolute;
      left: 0;
      right: 0;
      bottom: 100%;
      height: 200vh;
      z-index: -1;
      background: fade(@fl-body-primary-color, 90%);
      pointer-events: none;
      opacity: 0;
      .transition(opacity 0.3s);
    }
    & > li > a {
      background: #fff;
      font-size: 16px;
      padding: 15px 20px;

      & .fa {
        font-size: 16px;
        margin-right: 10px;
      }
    }
    & .divider {
      margin: 0;
    }

    .open & {
      bottom: 0;

      &:before {
        opacity: 1;
        pointer-events: auto;
      }
    }
  }
}

// ------------------------------------
// Mixins

.expand-dropdown() {
  & .dropdown-toggle {
    display: none;
  }
  & .dropdown-menu {
    display: block;
    border: 0;
    width: auto;
    margin: 0;
    padding: 0;
    min-width: 0;
    float: none;
    position: static;
    background: none;
    .box-shadow(none);
  }
}