mkdocs-material/src/assets/stylesheets/extensions/_footnotes.scss

////
/// Copyright (c) 2016 Martin Donath <martin.donath@squidfunk.com>
///
/// Permission is hereby granted, free of charge, to any person obtaining a
/// copy of this software and associated documentation files (the "Software"),
/// to deal in the Software without restriction, including without limitation
/// the rights to use, copy, modify, merge, publish, distribute, sublicense,
/// and/or sell copies of the Software, and to permit persons to whom the
/// Software is furnished to do so, subject to the following conditions:
///
/// The above copyright notice and this permission notice shall be included in
/// all copies or substantial portions of the Software.
///
/// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
/// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
/// FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
/// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
/// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
/// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
/// DEALINGS
////

// ----------------------------------------------------------------------------
// Footnotes extension
// ----------------------------------------------------------------------------

// Scoped in typesetted content for greater specificity
.md-content--typeset {

  // Footnote
  .footnote {
    color: $md-color-black--light;
    font-size: smaller;

    // Remove additional spacing on footnotes
    > ol {
      margin-left: 0;

      // Single footnote
      > li {

        // TODO: this doesn't work entirely
        // &::before {
        //   display: block;
        //   content: " ";
        //   padding-top: (5.6rem + 2.4rem + 0.4rem);
        //   margin-top: -(5.6rem + 2.4rem + 0.4rem);
        // }

        // Make back references visible on hover
        &:hover  .footnote-backref,
        &:target .footnote-backref {
          transform: translate3d(0, 0, 0);
          opacity: 1;
        }

        // Active or targeted back reference
        &:hover  .footnote-backref:hover,
        &:target .footnote-backref {
          color: $md-color-accent;
        }
      }
    }

    // Correct anchor offset
    &-ref::before {
      position: absolute;
      margin-top: -(5.6rem + 2.4rem + 0.4rem);
      padding-top: (5.6rem + 2.4rem + 0.4rem);
      content: " ";
      pointer-events: none;
    }

    // Make back reference text transparent for icon
    &-backref {
      @extend %md-icon;

      position: absolute;
      transform: translate3d(0.5rem, 0, 0);
      transition: transform 0.25s  0.125s,
                  color     0.25s,
                  opacity   0.125s 0.125s;
      color: $md-color-black--lighter;
      font-size: 2.0rem;
      opacity: 0;
      vertical-align: middle;

      // Hack: remove Unicode arrow for icon
      &::first-letter {
        font-size: 0;
      }

      // Back reference icon
      &::after {
        content: "keyboard_return";
      }
    }
  }
}