diff --git a/scripts/check-control-ui-performance.mts b/scripts/check-control-ui-performance.mts
index 793255d5f26e..ab71835b4107 100644
--- a/scripts/check-control-ui-performance.mts
+++ b/scripts/check-control-ui-performance.mts
@@ -29,9 +29,9 @@ const controlUiPerformanceBudgets = {
   // 350 KiB maintainer-approved by Vyctor 2026-08-11 for #121686;
   // #121734 left main 6 B below the prior 319 KiB hard ceiling.
   startupJsGzipBytes: 350 * KIB,
-  // The Absolutely theme and Inbox update styling landed concurrently within
-  // 45 KiB alone, but their merged main tree is 46,092 B. Keep 500 B headroom.
-  startupCssGzipBytes: 45 * KIB + 512,
+  // 45 KiB CSS ceilings maintainer-approved 2026-07 alongside the interleaved
+  // sidebar zone styling; headroom over the ~36.5 KiB post-diet baseline.
+  startupCssGzipBytes: 45 * KIB,
   largestJsGzipBytes: 215 * KIB,
   // Composer multiline surface (stack #124301) legitimately grew boot CSS;
   // operator decision 2026-08-25 rejected boot splitting due to precedence risk.