Fix the z-index value of the nav-tab inside card-tab #1933 (#1953)

Co-authored-by: Paweł Kuna <1282324+codecalm@users.noreply.github.com>

.changeset/slimy-queens-pull.md

@@ -0,0 +1,5 @@
+---
+"@tabler/core": patch
+---
+
+Fix the `z-index` value of the `nav-tab` inside `card-tab` #1933

src/scss/_variables.scss

@@ -605,6 +605,8 @@ $card-header-tabs-bg: var(--#{$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;