gnome-shell/data/theme/gnome-shell-sass/_drawing.scss

// Drawing mixins

// generic drawing of more complex things

@function draw_widget_edge($c:$borders_edge) {
// outer highlight "used" on most widgets
  @return 0 1px $c;
}

// provide font size in rem, with px fallback
@mixin fontsize($size: 24, $base: 16) {
  font-size: round($size) + pt;
  //font-size: ($size / $base) * 1rem;
}

@mixin draw_shadows($shadow1, $shadow2:none, $shadow3:none, $shadow4:none) {
//
// Helper function to stack up to 4 box-shadows;
//
  @if $shadow4!=none { box-shadow: $shadow1, $shadow2, $shadow3, $shadow4; }
  @else if $shadow3!=none { box-shadow: $shadow1, $shadow2, $shadow3; }
  @else if $shadow2!=none { box-shadow: $shadow1, $shadow2; }
  @else { box-shadow: $shadow1; }
}

// entries

@mixin entry($t, $fc:$selected_bg_color, $edge: $borders_edge) {
//
// Entries drawing function
//
// $t: entry type
// $fc: focus color
// $edge: set to none to not draw the bottom edge or specify a color to not use the default one
//
// possible $t values:
// normal, focus, insensitive
//

  @if $t==normal {
    background-color: $base_color;
    border-color: $borders_color;
  }
  @if $t==focus {
    border-color: if($fc==$selected_bg_color,
              $selected_borders_color,
              darken($fc,35%));
    box-shadow: inset 0 0 0 2px $fc;
  }
  @if $t==hover { }
  @if $t==insensitive {
    color: $insensitive_fg_color;
    border-color: $insensitive_bg_color;
    box-shadow: none;
  }
}

// On-screen Keyboard
@mixin keyboard_key($t, $c:$osd_bg_color, $tc:$osd_fg_color) {
//
// Keyboard key drawing function
//
// $t:    key type,
// $c:    base key color for colored* types
// $tc:   optional text color for colored* types
//
// possible $t values:
// normal, hover, active, insensitive, insensitive-active,
// backdrop, backdrop-active, backdrop-insensitive, backdrop-insensitive-active,
// osd, osd-hover, osd-active, osd-insensitive, osd-backdrop, undecorated
//

  // normal key
  @if $t==normal {
    color: $tc;
    background-color: lighten($c, 3%);
  }

  // focused key
  @if $t==focus {
    color: $tc;
    background-color: mix(lighten($c, 3%), $selected_bg_color, 90%);
    box-shadow: inset 0 0 0 2px transparentize($selected_bg_color, 0.4);
    &:hover {
      background-color: mix(lighten($c, 8%), $selected_bg_color, 90%);
      box-shadow: inset 0 0 0 2px transparentize($selected_bg_color, 0.3);
    }
  }

  // hover key
  @else if $t==hover {
    color: $tc;
    background-color: lighten($c, if($variant == 'light', 8%, 5%));
  }

  // active key
  @else if $t==active {
    color: $tc;
    background-color: darken($c,3%);
  }

  // insensitive key
  @else if $t==insensitive {
    color: $insensitive_fg_color;
    background-color: $insensitive_bg_color;
  }

  // reset
  @else if $t==undecorated {
    background-color: transparent;
    background-image: none;
  }
}


// buttons
// since buttons are all flat an borderless now the mixin is simpler

@mixin button($t, $tc:$fg_color, $c:$bg_color) {
//
// Button drawing function
//
// $t:    button type,
// $c:    base button colors, derived from fg_color
// $tc:    base button colors, derived from fg_color
//
// possible $t values:
// normal, hover, active, insensitive, insensitive-active,
// backdrop, backdrop-active, backdrop-insensitive, backdrop-insensitive-active,
// osd, osd-hover, osd-active, osd-insensitive, osd-backdrop, undecorated
//

  // normal button
  @if $t==normal {
    color: $tc;
    background-color: mix($tc, $c, 5%);
  }

  // focused button
  @if $t==focus {
    color: $tc;
    background-color: mix(mix($tc, $c, 5%), $selected_bg_color, 90%);
    // border-color: lighten($tc, 3%);
    box-shadow: inset 0 0 0 2px transparentize($selected_bg_color, 0.4);
    &:hover {
      background-color: mix(mix($tc, $c, 7%), $selected_bg_color, 90%);
      box-shadow: inset 0 0 0 2px transparentize($selected_bg_color, 0.3);
    }
  }

  // hover button
  @else if $t==hover {
    color: $tc;
    background-color: mix($tc, $c, 7%);
  }

  // active button
  @else if $t==active {
    color: $tc;
    background-color: mix($tc, $c, 2%);
  }

  // insensitive button
  @else if $t==insensitive {
    color: transparentize($tc, 0.5);
    background-color: transparentize($tc, .95);
  }

  // default/suggested button
  @else if $t==default {
    background-color: $selected_bg_color;
    color: $selected_fg_color;
    &:focus {
      box-shadow: inset 0 0 0 2px transparentize($selected_bg_color, 0.4);
    }
    &:hover, &:focus { 
      background-color: lighten($selected_bg_color, 5%);
      color: lighten($selected_fg_color, 5%);
    }
    &:active {
      background-color: darken($selected_bg_color, 7%);
      color: darken($selected_fg_color, 7%);
    }
    &:insensitive {
      @include button(insensitive);
      background-color: transparentize($selected_bg_color, .5);
      color: transparentize($selected_fg_color, .5);
    }
  }
  // reset
  @else if $t==undecorated {
    background-color: transparent;
    background-color: none;
  }
}

// tile
@mixin tile($color) {
  @extend %tile;
  background-color: transparent;

  &:hover,
  &:selected:hover {
    background-color: transparentize($color, .85);
  }

  &:focus:hover {
    background-color: transparentize($color, .8);
  }

  &:selected,
  &:focus {
    background-color: transparentize($color, .9);
  }

  &:outlined,
  &:checked,
  &:active {
    background-color: transparentize(darken($osd_bg_color, 10%), .5);
  }
}


// overview icons
// mixin fo tiles in the overview
@mixin overview_icon($color) {
  .overview-icon {
    @extend %tile;
    color: $color;
  }

  &:hover,
  &:focus:hover,
  &:selected {
    .overview-icon {
      background-color: transparentize($color, .9);
    }
  }

  &:focus {
    .overview-icon {
      background-color: transparentize($color, .95);
      // border-color: $selected_bg_color;
    }
  }

  &:drop {
    .overview-icon {
      border: 2px solid transparentize($selected_bg_color, .2); //already 2px transparent so no jumping
      background-color: transparentize($selected_bg_color, .8);
    }
  }

  &:active,
  &:focus:active,
  &:checked {
    .overview-icon {
      background-color: transparentize(darken($osd_bg_color, 10%), .5);
    }
  }
}


// styling for elements within popovers that look like notifications
@mixin card($flat: false) {
  border-radius: $base_border_radius;
  margin: $base_margin;
  box-shadow: 0 1px 1px 0 rgba(0,0,0,.1);

  @if $flat {
    @include button(undecorated);
    box-shadow: none !important;
  } @else {
    @include button(normal);
  }

  &:focus {
    @include button(focus);
  }

  &:hover {
    @include button(hover);
  }

  &:active {
    @include button(active);
  }
}