Remove invalid z-index setting for dropdown (#2036)

.changeset/eight-ladybugs-invite.md

@@ -0,0 +1,5 @@
+---
+"@tabler/core": patch
+---
+
+Remove invalid `z-index` setting for dropdowns

src/scss/_variables.scss

@@ -605,8 +605,6 @@ $card-header-tabs-bg: var(--#{$prefix}bg-surface-tertiary) !default;
 $cards-grid-gap: var(--#{$prefix}page-padding) !default;
 $cards-grid-breakpoint: lg !default;
 
-$zindex-dropdown: 1;
-
 // Carousel
 $carousel-control-color: $white !default;
 $carousel-control-icon-width: 1.5rem !default;