diff --git a/UI_UPDATE.MD b/UI_UPDATE.MD
index 9d5a7a3..e946f56 100644
--- a/UI_UPDATE.MD
+++ b/UI_UPDATE.MD
@@ -315,10 +315,12 @@ Always come back and update UI_UPDATE.MD once complete with task and task item.
 
 ### Sub-task 3.2: Advanced Breakpoint Management
 
-#### 3.2.1: Breakpoint Definition
-- [ ] Establish 6 responsive breakpoints (xs to 2xl)
-- [ ] Create breakpoint mixin system
-- [ ] Implement breakpoint-based CSS variables
+#### 3.2.1: Breakpoint Definition - COMPLETED 9/29/2025
+- [x] Establish 6 responsive breakpoints (xs to 2xl)
+- [x] Create breakpoint mixin system
+- [x] Implement breakpoint-based CSS variables
+
+**Notes:** Implemented comprehensive breakpoint system using CSS custom properties. Established 6 mobile-first breakpoints (xs: 320px, sm: 640px, md: 768px, lg: 1024px, xl: 1280px, 2xl: 1536px) in variables.css. Created breakpoint mixin system with custom property utilities (--mq-sm, --mq-md, etc.) and implemented all utility classes using var(--breakpoint-sm) in media queries across utilities.css. Added container max-widths and responsive padding variables for each breakpoint. Modernized all existing responsive utilities to use the new system, including grid, display, text alignment, and dimension utilities.
 
 #### 3.2.2: Responsive Typography
 - [ ] Create fluid typography scaling