NodeBB/public/scss/btn-ghost.scss

$btn-ghost-hover-color: mix($light, $dark, 90%)!default;
$btn-ghost-active-color: lighten($btn-ghost-hover-color, 5%)!default;
$btn-ghost-hover-color-dark: mix($dark, $light, 90%)!default;
$btn-ghost-active-color-dark: lighten($btn-ghost-hover-color-dark, 5%)!default;

:root {
	--btn-ghost-hover-color: #{$btn-ghost-hover-color};
	--btn-ghost-active-color: #{$btn-ghost-active-color};
}
[data-bs-theme="dark"] {
	--btn-ghost-hover-color: #{$btn-ghost-hover-color-dark};
	--btn-ghost-active-color: #{$btn-ghost-active-color-dark};
}

// https://getbootstrap.com/docs/5.3/components/buttons/#variables
.btn-ghost {
	--bs-btn-color: inherit!important;
	--bs-btn-bg: transparent;
	--bs-btn-border-color: transparent;
	--bs-btn-box-shadow: none;
	--bs-btn-hover-color: inherit;
	--bs-btn-hover-bg: #{$btn-ghost-hover-color};
	--bs-btn-hover-border-color: #{$btn-ghost-hover-color};
	--bs-btn-active-bg: #{$btn-ghost-hover-color};
	--bs-btn-active-border-color: transparent;
}