Fix Stepper heading alignment and overflow-menu separator on mobile

Make the StepperStep negative top-margin responsive on the same @xs/@lg
container breakpoints the heading text uses, so the number circle centers
on the heading's first line on narrow containers instead of being pulled
above it. Desktop (@lg) values are unchanged.

Guard the HeaderLinkMore overflow-menu separator on links.length > 0 so a
leading divider is not rendered on sites with social links but no header
links.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CcQvux7xUEEiGCKRsfm79k

packages/gitbook/src/components/DocumentView/StepperStep.tsx

@@ -21,11 +21,11 @@ export function StepperStep(props: BlockProps<DocumentBlockStepperStep>) {
         }
         switch (firstChild.type) {
             case 'heading-1':
-                return '-mt-9';
+                return '-mt-[18px] @xs:-mt-[24px] @lg:-mt-9';
             case 'heading-2':
-                return '-mt-[calc(1.25rem+1px)]';
+                return '-mt-[11px] @xs:-mt-[14px] @lg:-mt-[calc(1.25rem+1px)]';
             case 'heading-3':
-                return '-mt-[calc(0.50rem+1px)]';
+                return '-mt-[5px] @xs:-mt-[7px] @lg:-mt-[calc(0.50rem+1px)]';
             default:
                 return '';
         }

packages/gitbook/src/components/Header/HeaderLinkMore.tsx

@@ -45,7 +45,7 @@ export function HeaderLinkMore(props: {
                 {links.map((link, index) => (
                     <MoreMenuLink key={index} link={link} context={context} />
                 ))}
-                {socialAccounts.length > 0 && <DropdownMenuSeparator />}
+                {links.length > 0 && socialAccounts.length > 0 && <DropdownMenuSeparator />}
                 {socialAccounts.map((account) => (
                     <SocialAccountLink
                         key={`${account.platform}-${account.handle}`}