diff --git a/ZB.MOM.WW.Theme/Directory.Build.props b/ZB.MOM.WW.Theme/Directory.Build.props
index c8fbcf1..ad02954 100644
--- a/ZB.MOM.WW.Theme/Directory.Build.props
+++ b/ZB.MOM.WW.Theme/Directory.Build.props
@@ -4,7 +4,7 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <LangVersion>latest</LangVersion>
-    <Version>0.4.0</Version>
+    <Version>0.4.1</Version>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
   </PropertyGroup>
 </Project>
diff --git a/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css b/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css
index f5b0509..dd30161 100644
--- a/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css
+++ b/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css
@@ -226,14 +226,29 @@
     text-decoration: none;
 }
 /* Full-width modifier for a rail-foot action (sign in / sign out), composed as
-   class="rail-btn rail-btn-block". Block + width:auto fills the rail inside the
-   same 0.6rem inset .rail-btn already carries. Deliberately NOT width:100% —
-   that resolves against the containing block and then *adds* the 1.2rem of side
-   margin, overflowing the rail. Apps that hand-rolled this override hit exactly
-   that. */
+   class="rail-btn rail-btn-block".
+
+   The width is explicit — calc(100% - 1.2rem) — and NOT one of the two obvious
+   shorthands, because a rail foot typically holds BOTH element types: Sign In
+   is an <a>, Sign Out is a form-submit <button>. Each shorthand breaks one:
+
+     width: 100%   overflows. It resolves against the containing block and then
+                   .rail-btn's 0 0.6rem side margins are ADDED on top, pushing
+                   the control ~1.2rem past the rail edge (measured: 10px of
+                   visible clipping on a 197px rail).
+     width: auto   shrink-wraps a <button>. A form control does not take the
+                   fill-available behaviour a non-replaced block box like <a>
+                   gets, so the anchor filled and the button came up 114px short
+                   in the same container. That asymmetry is worse than the
+                   overflow it replaced, because the button is the one signed-in
+                   operators see.
+
+   calc() gets both right (measured 0px short for <a> and <button> alike). The
+   1.2rem must stay in step with .rail-btn's side margins above. */
 .rail-btn-block {
     display: block;
-    width: auto;
+    box-sizing: border-box;
+    width: calc(100% - 1.2rem);
     text-align: center;
 }