css/modules/primer-navigation/lib/menu.scss

// Side menu
//
// A menu on the side of a page, defaults to left side. e.g. github.com/about

.menu {
  margin-bottom: 15px;
  list-style: none;
  background-color: $bg-white;
  border: 1px solid $gray-300;
  border-radius: 3px;
}

.menu-item {
  position: relative;
  display: block;
  padding: $spacer-2 10px;
  border-bottom: 1px solid $gray-200;

  &:first-child {
    border-top: 0;
    border-top-left-radius: 2px;
    border-top-right-radius: 2px;

    &::before { border-top-left-radius: 2px; }
  }

  &:last-child {
    border-bottom: 0;
    border-bottom-right-radius: 2px;
    border-bottom-left-radius: 2px;

    &::before { border-bottom-left-radius: 2px; }
  }

  &:hover {
    text-decoration: none;
    background-color: $gray-100;
  }

  &.selected {
    font-weight: $font-weight-bold;
    color: $text-gray-dark;
    cursor: default;
    background-color: $bg-white;

    &::before {
      position: absolute;
      top: 0;
      bottom: 0;
      left: 0;
      width: 2px;
      content: "";
      background-color: $orange-600;
    }
  }

  .octicon {
    width: 16px;
    margin-right: 5px;
    color: $text-gray-dark;
    text-align: center;
  }

  .Counter {
    float: right;
    margin-left: 5px;
  }

  .menu-warning {
    float: right;
    color: $red-900;
  }

  .avatar {
    float: left;
    margin-right: 5px;
  }

  &.alert {
    .Counter {
      color: $text-red;
    }
  }
}

.menu-heading {
  display: block;
  padding: $spacer-2 10px;
  margin-top: 0;
  margin-bottom: 0;
  font-size: 13px;
  font-weight: $font-weight-bold;
  line-height: 20px;
  color: $gray-600;
  background-color: darken($gray-100, 1%);
  border-bottom: 1px solid $gray-200;

  &:hover {
    text-decoration: none;
  }

  &:first-child {
    border-top-left-radius: 2px;
    border-top-right-radius: 2px;
  }

  &:last-child {
    border-bottom: 0;
    border-bottom-right-radius: 2px;
    border-bottom-left-radius: 2px;
  }
}