diff --git a/components/header.tsx b/components/header.tsx
index b00fc0e..ce60c4c 100644
--- a/components/header.tsx
+++ b/components/header.tsx
@@ -4,8 +4,10 @@ import { Menu, X } from "lucide-react"
 import Link from "next/link"
 import { usePathname } from "next/navigation"
 import * as React from "react"
+import { createPortal } from "react-dom"
 
 import { Button } from "@/components/ui/button"
+import { useHeaderOffset } from "@/lib/hooks/useHeaderOffset"
 import { cn } from "@/lib/utils"
 
 const navigation = [
@@ -22,7 +24,9 @@ const navigation = [
 export function Header() {
   const [mobileMenuOpen, setMobileMenuOpen] = React.useState(false)
   const [scrolled, setScrolled] = React.useState(false)
+  const [mounted, setMounted] = React.useState(false)
   const pathname = usePathname()
+  const headerOffset = useHeaderOffset() ?? 64
 
   React.useEffect(() => {
     const handleScroll = () => {
@@ -32,6 +36,23 @@ export function Header() {
     return () => window.removeEventListener("scroll", handleScroll)
   }, [])
 
+  React.useEffect(() => {
+    setMounted(true)
+  }, [])
+
+  React.useEffect(() => {
+    if (!mobileMenuOpen) {
+      return
+    }
+
+    const previousOverflow = document.body.style.overflow
+    document.body.style.overflow = "hidden"
+
+    return () => {
+      document.body.style.overflow = previousOverflow
+    }
+  }, [mobileMenuOpen])
+
   return (
     <header
       className={cn(
@@ -41,7 +62,7 @@ export function Header() {
           : "bg-transparent"
       )}
     >
-      <nav className="section-container flex items-center justify-between py-4">
+      <nav className="section-container flex items-center justify-between py-4" data-header-height>
         <div className="flex lg:flex-1">
           <Link href="/" className="-m-1.5 p-1.5">
             <span className="text-xl font-bold tracking-tight">Mathis Group</span>
@@ -53,6 +74,8 @@ export function Header() {
             size="icon"
             onClick={() => setMobileMenuOpen(!mobileMenuOpen)}
             aria-label="Toggle menu"
+            aria-expanded={mobileMenuOpen}
+            aria-controls="mobile-nav"
           >
             {mobileMenuOpen ? (
               <X className="size-6" />
@@ -80,27 +103,34 @@ export function Header() {
       </nav>
 
       {/* Mobile menu */}
-      {mobileMenuOpen && (
-        <div className="lg:hidden">
-          <div className="space-y-1 border-t border-border p-6">
-            {navigation.map((item) => (
-              <Link
-                key={item.name}
-                href={item.href}
-                className={cn(
-                  "block rounded-md px-3 py-2 text-base font-medium transition-colors hover:bg-accent",
-                  pathname === item.href
-                    ? "bg-accent text-foreground"
-                    : "text-muted-foreground"
-                )}
-                onClick={() => setMobileMenuOpen(false)}
-              >
-                {item.name}
-              </Link>
-            ))}
-          </div>
-        </div>
-      )}
+      {mounted &&
+        mobileMenuOpen &&
+        createPortal(
+          <div
+            id="mobile-nav"
+            className="fixed inset-x-0 bottom-0 z-50 overflow-y-auto border-t border-border bg-background/95 shadow-lg backdrop-blur supports-[backdrop-filter]:bg-background/80 lg:hidden"
+            style={{ top: headerOffset }}
+          >
+            <div className="section-container space-y-1 py-6">
+              {navigation.map((item) => (
+                <Link
+                  key={item.name}
+                  href={item.href}
+                  className={cn(
+                    "block rounded-md px-3 py-2 text-base font-medium transition-colors hover:bg-accent",
+                    pathname === item.href
+                      ? "bg-accent text-foreground"
+                      : "text-muted-foreground"
+                  )}
+                  onClick={() => setMobileMenuOpen(false)}
+                >
+                  {item.name}
+                </Link>
+              ))}
+            </div>
+          </div>,
+          document.body
+        )}
     </header>
   )
 }
diff --git a/lib/hooks/useHeaderOffset.ts b/lib/hooks/useHeaderOffset.ts
index b327ec0..4894b80 100644
--- a/lib/hooks/useHeaderOffset.ts
+++ b/lib/hooks/useHeaderOffset.ts
@@ -16,13 +16,15 @@ export function useHeaderOffset(additionalOffset = 0) {
     }
 
     const updateOffset = () => {
-      const header = document.querySelector<HTMLElement>("header")
-      if (!header) {
+      const target =
+        document.querySelector<HTMLElement>("[data-header-height]") ??
+        document.querySelector<HTMLElement>("header")
+      if (!target) {
         setOffset(additionalOffset)
         return
       }
 
-      const { height } = header.getBoundingClientRect()
+      const { height } = target.getBoundingClientRect()
       setOffset(height + additionalOffset)
     }
 
@@ -31,10 +33,12 @@ export function useHeaderOffset(additionalOffset = 0) {
 
     let resizeObserver: ResizeObserver | null = null
     if (typeof ResizeObserver !== "undefined") {
-      const header = document.querySelector<HTMLElement>("header")
-      if (header) {
+      const target =
+        document.querySelector<HTMLElement>("[data-header-height]") ??
+        document.querySelector<HTMLElement>("header")
+      if (target) {
         resizeObserver = new ResizeObserver(updateOffset)
-        resizeObserver.observe(header)
+        resizeObserver.observe(target)
       }
     }