I've been looking at custom scss styling of Bootstrap 5 buttons using mixins. User ZIM's answer on the "How to change btn color in Bootstrap" post is very useful and clearly shows how the syntax for button-variant works.

However, I can't find any clear explanation on how the gradient inside that mixin works (as per the Bootstrap 5 docs).

There is an @include gradient-bg($background) in the mixin example on the buttons page and I can't seem to figure out how to pass a linear gradient to this or how to include it in a hypothetical ".btn-custom" class? Furthermore, how would a hover class with a different gradient background be defined using button-variant?

@mixin button-variant(
  $background,
  $border,
  $color: color-contrast($background),
  $hover-background: if($color == $color-contrast-light, shade-color($background, $btn-hover-bg-shade-amount), tint-color($background, $btn-hover-bg-tint-amount)),
  $hover-border: if($color == $color-contrast-light, shade-color($border, $btn-hover-border-shade-amount), tint-color($border, $btn-hover-border-tint-amount)),
  $hover-color: color-contrast($hover-background),
  $active-background: if($color == $color-contrast-light, shade-color($background, $btn-active-bg-shade-amount), tint-color($background, $btn-active-bg-tint-amount)),
  $active-border: if($color == $color-contrast-light, shade-color($border, $btn-active-border-shade-amount), tint-color($border, $btn-active-border-tint-amount)),
  $active-color: color-contrast($active-background),
  $disabled-background: $background,
  $disabled-border: $border,
  $disabled-color: color-contrast($disabled-background)
) {
  color: $color;
  @include gradient-bg($background);
  border-color: $border;
  @include box-shadow($btn-box-shadow);

  &:hover {
    color: $hover-color;
    @include gradient-bg($hover-background);
    border-color: $hover-border;
  }

Could someone explain this part of the mixin please?

Thanks in advance.