Various fixes (#11448)

# Scrollbar fix

Fixes https://github.com/twentyhq/twenty/issues/11403

<img width="1512" alt="image"
src="https://github.com/user-attachments/assets/b13fe0f2-8c61-4ea8-9ea1-e61e571a90da"
/>

---------

Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

packages/twenty-front/src/modules/ui/layout/page/components/DefaultLayout.tsx

@@ -26,7 +26,7 @@ const StyledLayout = styled.div`
   flex-direction: column;
   height: 100dvh;
   position: relative;
-  scrollbar-color: ${({ theme }) => theme.border.color.medium};
+  scrollbar-color: ${({ theme }) => theme.border.color.medium} transparent;
   scrollbar-width: 4px;
   width: 100%;
 
@@ -105,7 +105,9 @@ export const DefaultLayout = () => {
             )}
             {showAuthModal ? (
               <>
-                <SignInBackgroundMockPage />
+                <StyledMainContainer>
+                  <SignInBackgroundMockPage />
+                </StyledMainContainer>
                 <AnimatePresence mode="wait">
                   <LayoutGroup>
                     <AuthModal isOpenAnimated={animateModal}>