devdocs/assets/stylesheets/components/_header.scss

//
// Header
//

._header {
  position: absolute;
  z-index: var(--headerZ);
  top: 0;
  left: 0;
  display: -ms-flexbox;
  display: flex;
  width: var(--sidebarWidth);
  height: var(--headerHeight);
  background: var(--headerBackground);
  border-bottom: 1px solid var(--headerBorder);
  border-right: 1px solid var(--headerBorder);
  @extend %border-box;
  @extend %user-select-none;

  @include mobile { width: var(--sidebarMediumWidth); }
}

._header-left {
  float: left;
  height: 100%;
}

._header-right {
  float: right;
  height: 100%;
}

._header-btn {
  position: relative;
  flex: 0 0 auto;
  width: 2.25rem;
  height: 100%;
  color: var(--textColorLight);
  text-align: center;

  &[hidden] { display: none; }

  &[disabled] {
    opacity: .3;
    cursor: not-allowed;
  }

  > svg {
    width: 1.5rem;
    height: 1.5rem;
    @extend %svg-icon;
  }
}

//
// Menu
//

._menu {
  position: absolute;
  z-index: 1;
  top: .25rem;
  right: .25rem;
  width: 8.5rem;
  height: calc(13.75rem + 1px);
  white-space: nowrap;
  word-wrap: normal;
  overflow-wrap: normal;
  font-size: .875rem;
  background: var(--contentBackground);
  border: 1px solid var(--headerBorder);
  border-radius: 3px;
  box-shadow: -1px 1px 1px rgba(black, .05);
  transition: all 0ms cubic-bezier(0.23, 1, 0.32, 1) 1ms;
  opacity: 0;
  -webkit-transform: scale(0, 0);
          transform: scale(0, 0);
  -webkit-transform-origin: 100% 0;
          transform-origin: 100% 0;

  &.active {
    transition-duration: 250ms;
    opacity: 1;
    -webkit-transform: scale(1, 1);
            transform: scale(1, 1);
  }

  &:focus-within,
  ._menu-btn:focus + & {
    transition-duration: 250ms;
    opacity: 1;
    -webkit-transform: scale(1, 1);
            transform: scale(1, 1);
  }
}

._menu-title {
  margin: 0;
  line-height: 1.5rem;
  font-size: 1rem;
  font-weight: var(--boldFontWeight);
  letter-spacing: -.5px;
  background: var(--sidebarBackground);
  border-bottom: 1px solid var(--sidebarBorder);
  border-radius: 2px 2px 0 0;
}

._menu-title-link,
._menu-title-link:hover {
  display: block;
  padding: .5rem 1rem;
  color: var(--focusText);
  text-decoration: none;
}

._menu-link {
  display: block;
  padding: 0 1rem;
  line-height: 2.25rem;
  color: inherit;
  text-decoration: none;

  &:hover {
    color: var(--focusText);
    text-decoration: none;
    background: var(--sidebarBackground);
  }

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

//
// Search form
//

._search {
  -ms-flex: 1 1 auto;
      flex: 1 1 auto;
  position: relative;
  height: 100%;
  padding: .5rem 0 .5rem .5rem;
  @extend %border-box;

  > svg {
    position: absolute;
    z-index: 1;
    top: .875rem;
    left: .875rem;
    width: 1.25rem;
    height: 1.25rem;
    opacity: .42;
    @extend %svg-icon;

    fill: var(--absolute);
  }
}

._search-input {
  position: relative;
  display: block;
  width: 100%;
  height: 100%;
  padding: 0 .75rem 1px 1.75rem;
  font-size: .875rem;
  background: var(--contentBackground);
  border: 1px solid;
  border-color: var(--searchBorder);
  border-radius: 3px;

  &:focus {
    outline: 0;
    border-color: var(--inputFocusBorder);
    box-shadow: 0 0 1px var(--inputFocusBorder);
  }

  &[disabled] {
    background: var(--sidebarBackground);
    cursor: not-allowed;
  }
}

._search-clear {
  display: none;
  position: absolute;
  top: .5em;
  right: 0;
  width: 1.75rem;
  height: 2rem;
  opacity: .42;
  @extend %hide-text;

  &:hover { opacity: .7; }

  > svg {
    position: absolute;
    top: .5rem;
    left: .375rem;
    @extend %svg-icon;
    fill: var(--absolute);
  }

  ._search-active > & { display: block; }
}

._search-tag {
  display: none;
  position: absolute;
  z-index: 2;
  top: .875rem;
  left: .875rem;
  padding: 0 .375rem;
  line-height: 1.25rem;
  max-width: 50%;
  font-size: .8125rem;
  color: var(--textColorLight);
  background: var(--searchTagBackground);
  border-radius: 2px;
  @extend %truncate-text;
}