feat: add css variables for spacing (#1165)

Author: steveblue

projects/swimlane/ngx-ui/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## HEAD (unreleased)
 
+- Feature: New spacing CSS variables
+
 ## 51.0.0-alpha.3 (2025-11-10)
 
 - Fix (`ngx-dialog`): Default border radius for dialog that could interfere with custom template.

projects/swimlane/ngx-ui/src/lib/styles/layouts/_vars.scss

@@ -3,14 +3,18 @@
   --spacing-0: 0px;
   --spacing-2: 2px;
   --spacing-4: 4px;
+  --spacing-6: 6px;
   --spacing-8: 8px;
   --spacing-10: 10px;
   --spacing-12: 12px;
+  --spacing-14: 14px;
   --spacing-16: 16px;
+  --spacing-18: 18px;
   --spacing-20: 20px;
   --spacing-24: 24px;
   --spacing-30: 30px;
   --spacing-36: 36px;
+  --spacing-40: 40px;
   --spacing-48: 48px;
 
   // Radius Gaps