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
////

// ----------------------------------------------------------------------------
// Rules
// ----------------------------------------------------------------------------

// Scoped in typesetted content to match specificity of regular content
.md-typeset {

  // Footnotes extension
  .footnote {
    color: $md-color-black--light;
    font-size: ms(-1);

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

    // Single footnote
    li {

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

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

  // Footnote reference with corrected anchor offset
  .footnote-ref::before {
    position: absolute;
    margin-top: -(5.6rem + 2.4rem);
    padding-top: (5.6rem + 2.4rem);
    content: "";
    pointer-events: none;
  }

  // Footnote back-reference
  .footnote-backref {
    @extend %md-icon;

    position: absolute;
    transform: translateX(0.5rem);
    transition:
      transform 0.25s  0.125s,
      color     0.25s,
      opacity   0.125s 0.125s;
    color: $md-color-black--lighter;
    font-size: 1.5625em;
    opacity: 0;
    vertical-align: middle;

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

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