diff --git a/CLAUDE.md b/CLAUDE.md
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+++ b/CLAUDE.md
@@ -140,6 +140,13 @@
 ```
 
 ## CSS and Styling Standards
+**CRITICAL: NEVER use flexbox. Use CSS Grid exclusively.**
+
+- ❌ **NEVER** use `display: flex` or any flex properties (`flex-shrink`, `flex-wrap`, `flex-grow`, `flex-direction`)
+- ✅ **ALWAYS** use `display: grid` with `grid-template-columns`, `grid-auto-flow`, `place-items`, etc.
+- ✅ For inline checkbox+label: `display: grid; grid-template-columns: 18px 1fr; align-items: center; gap: 8px;`
+- ✅ For centering: `display: grid; place-items: center;`
+
 **CRITICAL: NEVER use !important in CSS**
 
 - ❌ **NEVER** use `!important` flags in CSS - it's a lazy hack that creates technical debt