fix: use CSS variable for tooltip z-index instead of hardcoded value (#117)

* fix: use calc(var(--z-modal) + 10) for tooltip z-index instead of hardcoded value

The tooltip pseudo-elements used a hardcoded z-index: 1000, inconsistent with the theme's CSS variable pattern for layering. Instead of adding a new variable, this uses calc(var(--z-modal) + 10) so the tooltip z-index is always relative to the modal layer.

* retained new lines

Author: rohitrath0d

src/css/tooltip.css

@@ -11,7 +11,7 @@
     visibility: hidden;
     transition: opacity var(--transition-fast), transform var(--transition-fast), visibility var(--transition-fast);
     pointer-events: none;
-    z-index: 1000;
+    z-index: calc(var(--z-modal) + 10);
   }
 
   /* Text */