twbs--bootstrap/scss/mixins/_gradients.scss

// Gradients

@mixin gradient-bg($color) {
  @if $enable-gradients {
    background: $color linear-gradient(180deg, mix($body-bg, $color, 15%), $color) repeat-x;
  } @else {
    background-color: $color;
  }
}

// Horizontal gradient, from left to right
//
// Creates two color stops, start and end, by specifying a color and position for each color stop.
@mixin gradient-x($start-color: #555, $end-color: #333, $start-percent: 0%, $end-percent: 100%) {
  background-image: linear-gradient(to right, $start-color $start-percent, $end-color $end-percent);
  background-repeat: repeat-x;
}

// Vertical gradient, from top to bottom
//
// Creates two color stops, start and end, by specifying a color and position for each color stop.
@mixin gradient-y($start-color: #555, $end-color: #333, $start-percent: 0%, $end-percent: 100%) {
  background-image: linear-gradient(to bottom, $start-color $start-percent, $end-color $end-percent);
  background-repeat: repeat-x;
}

@mixin gradient-directional($start-color: #555, $end-color: #333, $deg: 45deg) {
  background-image: linear-gradient($deg, $start-color, $end-color);
  background-repeat: repeat-x;
}
@mixin gradient-x-three-colors($start-color: #00b3ee, $mid-color: #7a43b6, $color-stop: 50%, $end-color: #c3325f) {
  background-image: linear-gradient(to right, $start-color, $mid-color $color-stop, $end-color);
  background-repeat: no-repeat;
}
@mixin gradient-y-three-colors($start-color: #00b3ee, $mid-color: #7a43b6, $color-stop: 50%, $end-color: #c3325f) {
  background-image: linear-gradient($start-color, $mid-color $color-stop, $end-color);
  background-repeat: no-repeat;
}
@mixin gradient-radial($inner-color: #555, $outer-color: #333) {
  background-image: radial-gradient(circle, $inner-color, $outer-color);
  background-repeat: no-repeat;
}
@mixin gradient-striped($color: rgba(255,255,255,.15), $angle: 45deg) {
  background-image: linear-gradient($angle, $color 25%, transparent 25%, transparent 50%, $color 50%, $color 75%, transparent 75%, transparent);
}