devdocs/assets/stylesheets/components/_header.scss

//
// Header
//

._header {
  position: absolute;
  z-index: $headerZ;
  top: 0;
  left: 0;
  right: 0;
  height: $headerHeight;
  line-height: $headerHeight;
  text-shadow: 0 1px rgba(white, .5);
  background: -webkit-linear-gradient(top,       #f6f6f8, #e4e4e6);
  background:         linear-gradient(to bottom, #f6f6f8, #e4e4e6);
  box-shadow: inset 0 1px rgba(white, .8),  // top inner glow
              inset 0 -1px rgba(white, .3); // bottom inner glow
  @extend %user-select-none;

  a:focus { outline: 0; }
}

//
// Navigation menu
//

._nav {
  float: right;
  margin-right: .5rem;
  font-size: .875rem;
  color: lighten($textColor, 5%);
}

._nav-link,
._nav-link:hover {
  float: left;
  padding: 0 1.25rem;
  color: inherit;
  text-decoration: none;
  background-clip: padding-box;
  border: solid transparent;
  border-width: 0 1px;
}

._nav-current,
._nav-current:hover {
  color: lighten($textColor, 8%);
  background: -webkit-linear-gradient(top,       #e1e1e4, #f2f2f5);
  background:         linear-gradient(to bottom, #e1e1e4, #f2f2f5);
  border-color: rgba(black, .15);
  box-shadow: inset 0 1px rgba(black, .07),    // top border
              inset 0 1px 2px rgba(black, .1), // top inner shadow
              1px 0 rgba(white, .2),           // right glow
              -1px 0 rgba(white, .2);          // left glow
}

//
// Logo
//

._logo {
  position: relative;
  float: left;
  height: $headerHeight;
  margin: 0;
  line-height: inherit;
  font-size: inherit;

  &:before, &:after { // left border
    content: '';
    position: absolute;
    top: 0;
    bottom: 0;
    left: -1px;
    width: 1px;
    background: -webkit-linear-gradient(bottom, #b4b7bf, rgba(#b4b7bf, 0) 80%);
    background:         linear-gradient(to top, #b4b7bf, rgba(#b4b7bf, 0) 80%);
  }

  &:after { // left glow
    left: -2px;
    background: -webkit-linear-gradient(bottom, rgba(white, .4), rgba(white, 0) 80%);
    background:         linear-gradient(to top, rgba(white, .4), rgba(white, 0) 80%);
  }
}

//
// Search form
//

._search {
  position: relative;
  float: left;
  width: $sidebarWidth;
  height: 100%;
  padding: .625rem;
  border-right: 1px solid transparent;
  @extend %border-box;

  @media #{$mediumScreen} { width: $sidebarMediumWidth; }

  &:before {
    position: absolute;
    top: 1rem;
    left: 1rem;
    opacity: .5;
    @extend %icon, %icon-search;
  }
}

._search-input {
  display: block;
  width: 100%;
  height: 100%;
  padding: 0 .75rem 1px 1.625rem;
  font-size: .875rem;
  border: 1px solid;
  border-color: #b2b5bb #babbc5 #bebfc6;
  border-radius: 1rem;
  box-shadow: inset 0 1px 1px rgba(black, .1), // top inner shadow
              0 1px rgba(white, .3);           // bottom glow

  &:focus {
    outline: 0;
    border-color: #35b5f4 #35b5f4 #30aeee;
    box-shadow: inset 0 0 1px rgba(#35b5f4, .5), // inner glow
                0 0 2px rgba(#35b5f4, .8);       // outer glow
  }
}

._search-clear {
  display: none;
  position: absolute;
  top: .5em;
  right: .5em;
  padding: .5em;
  cursor: pointer;
  opacity: .3;

  &:hover { opacity: .5; }
  &:before { @extend %icon, %icon-clear; }
  ._search-active > & { display: block; }
}

._search-tag {
  display: none;
  position: absolute;
  top: .875rem;
  left: .875rem;
  margin: -1px 0 0 -1px;
  padding: 0 .625rem;
  line-height: 1.25rem;
  font-size: .875rem;
  background: #dfeafe;
  border: 1px solid #98aed8;
  border-radius: .75rem;
  box-shadow: inset 0 1px rgba(white, .2), // top inner glow
              0 1px rgba(black, .05);      // bottom shadow
}