twbs--bootstrap/scss/_alert.scss

//
// Base styles
//

.alert {
  // scss-docs-start alert-css-vars
  --#{$prefix}alert-bg: transparent;
  --#{$prefix}alert-padding-x: #{$alert-padding-x};
  --#{$prefix}alert-padding-y: #{$alert-padding-y};
  --#{$prefix}alert-margin-bottom: #{$alert-margin-bottom};
  --#{$prefix}alert-color: inherit;
  --#{$prefix}alert-border-color: transparent;
  --#{$prefix}alert-border: #{$alert-border-width} solid var(--#{$prefix}alert-border-color);
  --#{$prefix}alert-border-radius: #{$alert-border-radius};
  // scss-docs-end alert-css-vars

  position: relative;
  padding: var(--#{$prefix}alert-padding-y) var(--#{$prefix}alert-padding-x);
  margin-bottom: var(--#{$prefix}alert-margin-bottom);
  color: var(--#{$prefix}alert-color);
  background-color: var(--#{$prefix}alert-bg);
  border: var(--#{$prefix}alert-border);
  @include border-radius(var(--#{$prefix}alert-border-radius));
}

// Headings for larger alerts
.alert-heading {
  // Specified to prevent conflicts of changing $headings-color
  color: inherit;
}

// Provide class for links that match alerts
.alert-link {
  font-weight: $alert-link-font-weight;
}


// Dismissible alerts
//
// Expand the right padding and account for the close button's positioning.

.alert-dismissible {
  padding-right: $alert-dismissible-padding-r;

  // Adjust close link position
  .btn-close {
    position: absolute;
    top: 0;
    right: 0;
    z-index: $stretched-link-z-index + 1;
    padding: $alert-padding-y * 1.25 $alert-padding-x;
  }
}


// scss-docs-start alert-modifiers
// Generate contextual modifier classes for colorizing the alert.

@each $state, $value in $theme-colors {
  $alert-background: shift-color($value, $alert-bg-scale);
  $alert-border: shift-color($value, $alert-border-scale);
  $alert-color: shift-color($value, $alert-color-scale);

  @if (contrast-ratio($alert-background, $alert-color) < $min-contrast-ratio) {
    $alert-color: mix($value, color-contrast($alert-background), abs($alert-color-scale));
  }
  .alert-#{$state} {
    @include alert-variant($alert-background, $alert-border, $alert-color);
  }
}
// scss-docs-end alert-modifiers