diff --git a/src/scss/selectize.bootstrap3.scss b/src/scss/selectize.bootstrap3.scss
index 15d2fd414..180079107 100644
--- a/src/scss/selectize.bootstrap3.scss
+++ b/src/scss/selectize.bootstrap3.scss
@@ -21,7 +21,7 @@ $select-color-optgroup: $dropdown-bg;
 $select-color-optgroup-text: $dropdown-header-color;
 $select-color-optgroup-border: $dropdown-divider-bg;
 $select-color-dropdown: $dropdown-bg;
-$select-color-dropdown-border-top: mix($input-border, $input-bg, 0.8);
+$select-color-dropdown-border-top: mix($input-border, $input-bg, 80%);
 $select-color-dropdown-item-active: $dropdown-link-hover-bg;
 $select-color-dropdown-item-active-text: $dropdown-link-hover-color;
 $select-color-dropdown-item-create-active-text: $dropdown-link-hover-color;
diff --git a/src/scss/selectize.bootstrap4.scss b/src/scss/selectize.bootstrap4.scss
index cbe80687f..0c7fa1c3b 100644
--- a/src/scss/selectize.bootstrap4.scss
+++ b/src/scss/selectize.bootstrap4.scss
@@ -29,7 +29,7 @@ $select-color-dropdown: $dropdown-bg !default;
 $select-color-dropdown-border-top: mix(
   $input-border-color,
   $input-bg,
-  0.8
+  80%
 ) !default;
 $select-color-dropdown-item-active: $dropdown-link-hover-bg !default;
 $select-color-dropdown-item-active-text: $dropdown-link-hover-color !default;
diff --git a/src/scss/selectize.bootstrap5.scss b/src/scss/selectize.bootstrap5.scss
index d21f3e92b..c3a2ccb02 100644
--- a/src/scss/selectize.bootstrap5.scss
+++ b/src/scss/selectize.bootstrap5.scss
@@ -29,7 +29,7 @@ $select-color-dropdown: $dropdown-bg !default;
 $select-color-dropdown-border-top: mix(
   $input-border-color,
   $input-bg,
-  0.8
+  80%
 ) !default;
 $select-color-dropdown-item-active: $dropdown-link-hover-bg !default;
 $select-color-dropdown-item-active-text: $dropdown-link-hover-color !default;