Try to fix the dropdown-toggle-split

scss/_button-group.scss

@@ -80,8 +80,23 @@
   &:not(:hover):not(:focus):not(:active) {
     border-left-color: transparent;
 
-    &.btn-inverse::before {
+    &.btn-inverse {
+      color: $white;
       background-color: $black;
+      border-color: $white;
+
+      &::before {
+        background-color: $black;
+      }
+    }
+  }
+
+  &:active,
+  &.active {
+    border-left: 2px solid $black !important; // stylelint-disable-line declaration-no-important
+
+    &.btn-inverse {
+      border-left: 2px solid $primary !important; // stylelint-disable-line declaration-no-important
     }
   }
 

scss/_buttons.scss

@@ -19,7 +19,7 @@
   --#{$variable-prefix}btn-border-radius: #{$btn-border-radius};
   --#{$variable-prefix}btn-box-shadow: #{$btn-box-shadow};
   --#{$variable-prefix}btn-disabled-opacity: #{$btn-disabled-opacity};
-  --#{$variable-prefix}btn-focus-box-shadow: 0 0 0 #{$btn-focus-width} rgba(var(--#{$variable-prefix}btn-focus-shadow-rgb), .5);
+  --#{$variable-prefix}btn-focus-box-shadow: 0 0 0 #{$btn-focus-width} var(--#{$variable-prefix}btn-focus-shadow-rgb); // Boosted mod
   --#{$boosted-variable-prefix}icon-spacing: #{$btn-icon-padding-x}; // Boosted mod
   // scss-docs-end btn-css-vars
 
@@ -79,16 +79,7 @@
     background-image: if($enable-gradients, none, null);
     border-color: var(--#{$variable-prefix}btn-active-border-color);
     outline-color: var(--#{$variable-prefix}btn-active-border-color); // Boosted mod
-    @include box-shadow(var(--#{$variable-prefix}btn-active-shadow));
-
-    &:focus {
-      // Avoid using mixin so we can pass custom focus shadow properly
-      @if $enable-shadows {
-        box-shadow: var(--#{$variable-prefix}btn-active-shadow), var(--#{$variable-prefix}btn-focus-box-shadow);
-      } @else {
-        box-shadow: var(--#{$variable-prefix}btn-focus-box-shadow);
-      }
-    }
+    // Boosted mod: no box shadow modification for the active state
   }
 
   &:disabled,
@@ -121,37 +112,37 @@
 .btn-warning {
   @include button-variant($primary, $primary, $active-background: $white, $active-border: $black);
   &.btn-inverse {
-    @include button-variant($primary, $primary, $black, $white, $white, $black, $black, $white, $white, $gray-700, $gray-700, $black);
+    @include button-variant($primary, $primary, $black, $white, $white, $black, $black, $white, $white, $gray-700, $gray-700, $black, true);
   }
 }
 
 .btn-light,
 .btn-secondary {
   @include button-variant($white, $black, $disabled-background: $white, $disabled-border: $gray-500, $disabled-color: $gray-500);
   &.btn-inverse {
-    @include button-variant($black, $white, $white, $white, $white, $black, $primary, $primary, $black, transparent, $gray-700, $gray-700);
+    @include button-variant($black, $white, $white, $white, $white, $black, $primary, $primary, $black, transparent, $gray-700, $gray-700, true);
   }
 }
 
 .btn-success {
   @include button-variant($success, $success);
   &.btn-inverse {
-    @include button-variant($success, $success, $black,  $white, $white, $black, $primary, $primary, $black, $gray-700, $gray-700, $black);
+    @include button-variant($success, $success, $black,  $white, $white, $black, $primary, $primary, $black, $gray-700, $gray-700, $black, true);
   }
 }
 
 .btn-info,
 .btn-dark {
   @include button-variant($black, $black, $white, $white, $black, $black);
   &.btn-inverse {
-    @include button-variant($white, $white, $black, $black, $white, $white, $primary, $primary, $black, $gray-700, $gray-700, $black);
+    @include button-variant($white, $white, $black, $black, $white, $white, $primary, $primary, $black, $gray-700, $gray-700, $black, true);
   }
 }
 
 .btn-danger {
   @include button-variant($danger, $danger);
   &.btn-inverse {
-    @include button-variant($danger, $danger, $white, $white, $white, $black, $primary, $primary, $black, $gray-700, $gray-700, $black);
+    @include button-variant($danger, $danger, $white, $white, $white, $black, $primary, $primary, $black, $gray-700, $gray-700, $black, true);
   }
 }
 // scss-docs-end btn-variant-loops

scss/mixins/_buttons.scss

@@ -4,6 +4,8 @@
 //
 // Easily pump out default styles, as well as :hover, :focus, :active,
 // and disabled options for all buttons
+//
+// Boosted mod: Extra parameter to handle inverted buttons and their box shadows
 
 // scss-docs-start btn-variant-mixin
 @mixin button-variant(
@@ -18,19 +20,26 @@
   $active-color: color-contrast($active-background),
   $disabled-background: $gray-500, // Boosted mod
   $disabled-border: $gray-500, // Boosted mod
-  $disabled-color: $white // Boosted mod
+  $disabled-color: $white, // Boosted mod
+  $inverted: false // Boosted mod
 ) {
   --#{$variable-prefix}btn-color: #{$color};
   --#{$variable-prefix}btn-bg: #{$background};
   --#{$variable-prefix}btn-border-color: #{$border};
   --#{$variable-prefix}btn-hover-color: #{$hover-color};
   --#{$variable-prefix}btn-hover-bg: #{$hover-background};
   --#{$variable-prefix}btn-hover-border-color: #{$hover-border};
-  --#{$variable-prefix}btn-focus-shadow-rgb: $border; // Boosted mod
+  // Boosted mod
+  @if $inverted {
+    --#{$variable-prefix}btn-focus-shadow-rgb: #{$color};
+  } @else {
+    --#{$variable-prefix}btn-focus-shadow-rgb: #{$hover-color};
+  }
+  // End mod
   --#{$variable-prefix}btn-active-color: #{$active-color};
   --#{$variable-prefix}btn-active-bg: #{$active-background};
   --#{$variable-prefix}btn-active-border-color: #{$active-border};
-  --#{$variable-prefix}btn-active-shadow: #{$btn-active-box-shadow};
+  // Boosted mod: no definition of --#{$variable-prefix}btn-active-shadow
   --#{$variable-prefix}btn-disabled-color: #{$disabled-color};
   --#{$variable-prefix}btn-disabled-bg: #{$disabled-background};
   --#{$variable-prefix}btn-disabled-border-color: #{$disabled-border};