KNACSS/sass/components/_alerts.scss

/* ----------------------------- */
/* ==Alerts                      */
/* ----------------------------- */
/* use .alert-- classes for variants */

.alert {
  padding: $spacer-small $spacer-small;
  margin-top: 0.75em;
  margin-bottom: 0;
  color: $color-base;
  border-radius: $border-radius;
  background-color: $color-muted;

  & a {
    color: inherit;
    text-decoration: underline;
  }
}

.alert {
  @each $name, $background-color, $color, $border in $variants-list {
    &--#{$name} {
      @extend .alert;
      background-color: $background-color;
      color: $color;
      box-shadow: $border;
    }
  }
}

// alert state variants
.alert {
  &--small {
    font-size: $font-size-base - 0.4rem;
  }

  &--big {
    font-size: $font-size-base + 0.4rem;
  }

  &--block {
    width: 100% !important;
    display: block;
  }
  &.disabled,
  &--disabled {
    opacity: 0.5;
    cursor: not-allowed;
  }
  &:empty {
    display: none;
  }
}