Add missing Bootstrap variables

src/assets/scss/_variables.scss

@@ -720,6 +720,10 @@ $hr-border-color: null !default; // Allows for inherited colors
 $hr-border-width: var(--#{$prefix}border-width) !default;
 $hr-opacity: 0.25 !default;
 
+// scss-docs-start vr-variables
+$vr-border-width:             var(--#{$prefix}border-width) !default;
+// scss-docs-end vr-variables
+
 $legend-margin-bottom: 0.5rem !default;
 $legend-font-size: 1.5rem !default;
 $legend-font-weight: null !default;
@@ -729,6 +733,7 @@ $dt-font-weight: $font-weight-bold !default;
 $list-inline-padding: 0.5rem !default;
 
 $mark-padding: 0.1875em !default;
+$mark-color:                  $body-color !default;
 $mark-bg: $yellow-100 !default;
 // scss-docs-end type-variables
 
@@ -850,6 +855,7 @@ $btn-active-box-shadow: inset 0 3px 5px rgba($black, 0.125) !default;
 $btn-link-color: var(--#{$prefix}link-color) !default;
 $btn-link-hover-color: var(--#{$prefix}link-hover-color) !default;
 $btn-link-disabled-color: $gray-600 !default;
+$btn-link-focus-shadow-rgb:   to-rgb(mix(color-contrast($link-color), $link-color, 15%)) !default;
 
 // Allows for customizing button radius independently from global border radius
 $btn-border-radius: var(--#{$prefix}border-radius) !default;