diff --git a/workspaces/theme/.changeset/bui-main-flex.md b/workspaces/theme/.changeset/bui-main-flex.md
new file mode 100644
index 00000000000..1c04297e443
--- /dev/null
+++ b/workspaces/theme/.changeset/bui-main-flex.md
@@ -0,0 +1,5 @@
+---
+'@red-hat-developer-hub/backstage-plugin-theme': patch
+---
+
+Make NFS BUI catalog entity `<main>` a flex column so Topology and Scorecard fill the content well instead of leaving a gap below short tab content (RHDHBUGS-3543).
diff --git a/workspaces/theme/plugins/theme/src/utils/createComponents.test.ts b/workspaces/theme/plugins/theme/src/utils/createComponents.test.ts
index 0b9f98de669..3ed80427159 100644
--- a/workspaces/theme/plugins/theme/src/utils/createComponents.test.ts
+++ b/workspaces/theme/plugins/theme/src/utils/createComponents.test.ts
@@ -117,6 +117,24 @@ describe('createComponents', () => {
     );
   });
 
+  it('makes NFS BUI main a flex column so nested Containers can grow', () => {
+    const actual = createComponents({ palette: customDarkTheme() });
+    const root = actual.BackstageSidebarPage?.styleOverrides?.root as
+      | Record<string, unknown>
+      | undefined;
+    const desktop = root?.['@media (min-width: 600px)'] as
+      | Record<string, unknown>
+      | undefined;
+    expect(desktop?.['& > main:not([data-backstage-core-page])']).toEqual(
+      expect.objectContaining({
+        display: 'flex',
+        flexDirection: 'column',
+        flex: 1,
+        minHeight: 0,
+      }),
+    );
+  });
+
   it('paints BUI content Containers with mainSectionBackgroundColor', () => {
     const actual = createComponents({ palette: customDarkTheme() });
     const root = actual.BackstageSidebarPage?.styleOverrides?.root as
diff --git a/workspaces/theme/plugins/theme/src/utils/createComponents.ts b/workspaces/theme/plugins/theme/src/utils/createComponents.ts
index 6f313f41d46..56c673adbb3 100644
--- a/workspaces/theme/plugins/theme/src/utils/createComponents.ts
+++ b/workspaces/theme/plugins/theme/src/utils/createComponents.ts
@@ -789,6 +789,18 @@ export const createComponents = (themeConfig: ThemeConfig): Components => {
               // Prevent overflow in the main container due to the margin
               maxHeight: `calc(100vh - 2 * ${general.pageInset})`,
             },
+            // NFS BUI entity pages wrap PluginHeader + tabs + Container in a
+            // classless <main>. BUI Container is flex: 1 1 0% but that only
+            // grows when main is a flex column — otherwise Topology / Scorecard
+            // stay content-height inside a tall well (RHDHBUGS-3543). Do not
+            // override Backstage Page, which uses display:grid on <main>.
+            '& > main:not([data-backstage-core-page])': {
+              display: 'flex',
+              flexDirection: 'column',
+              flex: 1,
+              minHeight: 0,
+              maxHeight: `calc(100% - 2 * ${general.pageInset})`,
+            },
             // NFS / BUI pages use Container instead of <main>. Match the content
             // well color (same token as BackstageContent) and rely on flex: 1
             // from BUI rather than 100vh so PluginHeader siblings are not overflowed.