gtk2/gtk/resources/theme/Adwaita/_drawing.scss

// Drawing mixins

// generic drawing of more complex things

$widget_edge: 0 1px $borders_edge; //outer hilight "used" on
                                   //most widgets

@mixin _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, $noedge:false) {
//
// Entries drawing function
//
// $t: entry type
// $fc: focus color
// $noedge: set to true not to draw the bottom edge hilight
//
// possible $t values:
// normal, focus, insensitive, backdrop, backdrop-insensitive;
//
  background-color: transparent;
  border-style: solid;
  border-width: 1px;
  background-image: linear-gradient(to bottom,
                                    darken($base_color,3%),
                                    $base_color 90%);
  // we need to match the same shadow types (inset/outset) in various states
  // hence transparent shadows istead of resetting them when not needed
  $_blank_inner_shadows: inset 0 2px 2px -2px
                           transparentize(mix(black, $base_color, 50%),1),
                         inset 0 0 2px 1px
                           transparentize(mix($fc,$base_color,20%),1);

  $_blank_edge: if($noedge, none, 0 1px transparentize(white,1));
  $_entry_edge: if($noedge, none, $widget_edge);
  
  @if $t==normal {
    border-color: $borders_color;
    @include _shadows(inset 0 2px 2px -2px mix(black, $base_color, 50%),
                      inset 0 0 2px 1px
                        transparentize(mix($fc,$base_color, 20%),1),
                      $_entry_edge);
    // the second transparent shadow is needed for the transition to work
  }
  @if $t==focus {
    @if $variant == 'light' {
      border-color: $fc;
      @include _shadows(inset 0 2px 2px -2px mix(black, $base_color, 50%),
                        inset 0 0 2px 1px mix($fc,$base_color, 20%),
                        $_entry_edge);
    }
    @else {
      border-color: if($fc==$selected_bg_color,
                       $selected_borders_color,
                       darken($fc,35%));
      @include _shadows(inset 0 2px 2px -2px mix(black, $base_color, 50%),
                        inset 0 0 1px 1px $fc,
                        $_entry_edge);
    }
  }
  @if $t==insensitive {
    color: $insensitive_fg_color;
    border-color: $borders_color;
    background-image: linear-gradient(to bottom, $insensitive_bg_color);
    @include _shadows($_blank_inner_shadows, $_entry_edge);

  }
  @if $t==backdrop {
    color: $backdrop_fg_color;
    background-image: linear-gradient(to bottom, $backdrop_base_color);
    @include _shadows($_blank_inner_shadows, $_blank_edge);
  }
  @if $t==backdrop-insensitive {
    color: $backdrop_insensitive_color;
    background-image: linear-gradient(to bottom, $backdrop_bg_color);
    @include _shadows($_blank_inner_shadows, $_blank_edge);
  }
}

// buttons

@function _border_color ($c) { @return darken($c,25%); } // colored buttons want the border form the base color

@mixin _button_text_shadow ($tc:$fg_color, $bg:$bg_color) {
//
// helper function for the text emboss effect
//
// $tc is the optional text color, not the shadow color
//
// TODO: this functions needs a way to deal with special cases
//

  $_lbg: lightness($bg)/100%;

  $_dark: transparentize(black,$_lbg*0.8);
  $_bright: transparentize(white,1-$_lbg/($_lbg*1.3));

  @if lightness($tc) < 50% {
    text-shadow: 0 1px $_bright;
    icon-shadow: 0 1px $_bright;
  }
  @else {
    text-shadow: 0 -1px $_dark;
    icon-shadow: 0 -1px $_dark;
  }
}

@mixin button($t, $c:$bg_color, $tc:$fg_color, $noedge:false) {
//
// Button drawing function
//
// $t:  button type,
// $c:  base button color for colored* types
// $tc: optional text color for colored* types
// $noedge: set to true not to draw the bottom edge hilight
//
// possible $t values:
// normal, hover, active, insensitive, insensitive-active,
// backdrop, backdrop-active, backdrop-insensitive, backdrop-insensitive-active,
// osd, osd-hover, osd-active, osd-insensitive, undecorated
//
  border-style: solid;

  $_top_hilight: if(lightness($c)> 70%, white, transparentize(white,0.9)); //not just dark/light but colored buttons

  @if $t==normal {
  //
  // normal button
  //
    border-width: 1px;
    color: $tc;
    background-image: linear-gradient(to bottom,
                                  lighten($c,5%),
                                  $c 40%,
                                  darken($c,5%)
                                  );

    @if $c!=$bg_color { border-color: _border_color($c); }
    @else { border-color: $borders_color; }

    @include _button_text_shadow($tc,$c);
    $_outsets: if($noedge, none, $widget_edge);
    @include _shadows(inset 0 1px $_top_hilight, $_outsets);
  }

  @else if $t==hover {
  //
  // hovered button
  //
    color: $tc;
    @if $c!=$bg_color { border-color: _border_color($c); }
    @else { border-color: $borders_color; }
    background-image: linear-gradient(to bottom,
                                      lighten($c,14%),
                                      lighten($c,4%) 40%,
                                      $c);

    @include _button_text_shadow($tc,lighten($c,4%));
    $_outsets: if($noedge, none, $widget_edge);
    @include _shadows(inset 0 1px $_top_hilight, $_outsets);
  }

  @else if $t==active {
  //
  // pushed button
  //
    color: $tc;
    @if $c!=$bg_color {border-color: _border_color($c); }
    @else { border-color: $borders_color; }
    background-image: linear-gradient(to bottom,
                                      darken($c,9%),
                                      darken($c,5%));
    @include _button_text_shadow($tc,darken($c,10%));
    $_outsets: if($noedge, none, $widget_edge);
    @include _shadows(inset 0 2px 1px -2px transparentize(black,0.4),$_outsets);
  }
  @else if $t==insensitive {
  //
  // insensitive button
  //
    color: $insensitive_fg_color;
    border-color: $insensitive_borders_color;
    background-image: linear-gradient(to bottom, $insensitive_bg_color);
    text-shadow: none;
    icon-shadow: none;
    $_outsets: if($noedge, none, $widget_edge);
    // white with 0 alpha to avoid an ugly transition, since no color means
    // black with 0 alpha
    @include _shadows(inset 0 1px transparentize(white,1), $_outsets);
  }
  @else if $t==insensitive-active {
  //
  // insensitive pushed button
  //
    color: $insensitive_fg_color;
    border-color: $insensitive_borders_color;
    background-image: linear-gradient(to bottom,
                        mix($insensitive_borders_color,
                            $insensitive_bg_color, 10%));
    $_outsets: if($noedge, none, $widget_edge);
    // white with 0 alpha to avoid an ugly transition, since no color means
    // black with 0 alpha
    @include _shadows(inset 0 1px transparentize(white,1), $_outsets);
  }

  @else if $t==backdrop {
  //
  // backdrop button
  //
    color: if($c!=$bg_color, $tc, $backdrop_fg_color);
    border-color: if($c!=$bg_color, $c, $backdrop_borders_color);
    background-image: linear-gradient(to bottom,
                                      if($c!=bg_color,$c,$backdrop_bg_color));
    text-shadow: none;
    icon-shadow: none;
    @include _shadows(inset 0 1px transparentize(white,1),
                            0 1px transparentize(white,1));
  }

  @else if $t==backdrop-active {
  //
  // backdrop pushed button
  //
    color: $backdrop_fg_color;
    border-color: $backdrop_borders_color;
    background-image: linear-gradient(to bottom,
                        mix($backdrop_borders_color,$backdrop_bg_color, 35%));
    box-shadow: inset 0 1px transparentize(white,1),
                0 1px transparentize(white,1);
  }

  @else if $t==backdrop-insensitive {
  //
  // backdrop insensitive button
  //
    color: $backdrop_insensitive_color;
    border-color: $backdrop_borders_color;
    background-image: linear-gradient(to bottom, $backdrop_bg_color);
    box-shadow: inset 0 1px transparentize(white,1),
                0 1px transparentize(white,1);
  }

  @else if $t==backdrop-insensitive-active {
  //
  // backdrop insensitive pushed button
  //
    color: $backdrop_insensitive_color;
    border-color: $backdrop_borders_color;
    background-image: linear-gradient(to bottom,
                        mix($backdrop_borders_color,$backdrop_bg_color, 8%));
    box-shadow: inset 0 1px transparentize(white,1),
                0 1px transparentize(white,1);
  }
  
  @else if $t==osd {
  //
  // normal osd button
  //
    background-image: linear-gradient(to bottom, $osd_bg_color);
    border-color: $osd_borders_color;
    box-shadow: none;
  }
  @else if $t==osd-hover {
  //
  // active osd button
  //
    background-image: linear-gradient(to bottom, lighten($osd_bg_color,10%));
    border-color: $osd_borders_color;
    box-shadow: none;
  }
  @else if $t==osd-active {
  //
  // active osd button
  //
    background-image: linear-gradient(to bottom, lighten($osd_bg_color,20%));
    border-color: $osd_borders_color;
    box-shadow: none;
  }
  @else if $t==osd-insensitive {
  //
  // insensitive osd button
  //
    border-color: $osd_borders_color;
    color: $insensitive_fg_color;
  }
  @else if $t==undecorated {
  //
  // reset
  //
    border-color: transparent;
    background-color: transparent;
    background-image: none;
    box-shadow: inset 0 1px transparentize(white,1);
    text-shadow: none;
    icon-shadow: none;
  } 
}

@mixin trough($flat:false, $c:$bg_color, $tc:$fg_color, $noedge:false) {
  color: mix($tc,$bg_color,80%);
  @if $flat { background-image: linear-gradient(to bottom,$c); }
  @else {
    background-image: linear-gradient(to bottom,
                                      mix(black,$c,15%) 5%,
                                      mix(black,$c,10%) 20%,
                                      mix(black,$c,10%) 90%,
                                      $c);
  }

  border-color: if($c!=$bg_color, _border_color($c), $border_color);
  
  @if not($noedge) { 
    @if lightness($c) > 60% {
      box-shadow: inset 0 -1px $borders_edge,
                  0 1px $borders_edge;
    }
    @else {
      box-shadow: inset 0 -1px transparentize($borders_edge,0.5),
                  0 1px transparentize($borders_edge,0.5);
    }
  }
  @else { box-shadow: none; }
}