diff --git a/.changeset/odd-beds-peel.md b/.changeset/odd-beds-peel.md
new file mode 100644
index 00000000..f6bed371
--- /dev/null
+++ b/.changeset/odd-beds-peel.md
@@ -0,0 +1,5 @@
+---
+'@ithaka/pharos-site': patch
+---
+
+Fix mobile sidenav
diff --git a/packages/pharos-site/src/components/Sidenav.tsx b/packages/pharos-site/src/components/Sidenav.tsx
index cb823a70..0746d410 100644
--- a/packages/pharos-site/src/components/Sidenav.tsx
+++ b/packages/pharos-site/src/components/Sidenav.tsx
@@ -1,4 +1,4 @@
-import { useLayoutEffect, useState } from 'react';
+import { useEffect, useLayoutEffect, useState } from 'react';
 import type { FC, ReactElement } from 'react';
 import { withPrefix, useStaticQuery, graphql } from 'gatsby';
 import { useLocation } from '@reach/router';
@@ -6,7 +6,12 @@ import { useLocation } from '@reach/router';
 import handleLinkClick from '../utils/handleLinkClick';
 import { siteBrand__title, siteBrand__subTitle, sidenav } from './Sidenav.module.css';
 
-const Sidenav: FC = () => {
+interface SidenavProps {
+  isOpen: boolean;
+  showCloseButton?: boolean;
+}
+
+const Sidenav: FC<SidenavProps> = ({ isOpen, showCloseButton }) => {
   const [Display, setDisplay] = useState<ReactElement | null>(null);
   const Pharos =
     typeof window !== `undefined` ? require('@ithaka/pharos/lib/react-components') : null;
@@ -23,7 +28,7 @@ const Sidenav: FC = () => {
     }
   `);
 
-  useLayoutEffect(() => {
+  useEffect(() => {
     const {
       PharosSidenav,
       PharosSidenavSection,
@@ -55,7 +60,13 @@ const Sidenav: FC = () => {
     };
 
     const content = (
-      <PharosSidenav mainContentId="skip-link" open={true} className={sidenav}>
+      <PharosSidenav
+        mainContentId="skip-link"
+        id="site-sidenav"
+        open={isOpen}
+        hasCloseButton={showCloseButton}
+        className={sidenav}
+      >
         <PharosLink href="/" slot="top" flex onClick={handleLinkClick}>
           <div>
             <div className={siteBrand__title}>{data.site.siteMetadata.title}</div>
@@ -167,7 +178,7 @@ const Sidenav: FC = () => {
     );
 
     setDisplay(content);
-  }, [Pharos, data, location]);
+  }, [Pharos, data, location, isOpen, showCloseButton]);
 
   return Display;
 };
diff --git a/packages/pharos-site/src/components/layout.module.css b/packages/pharos-site/src/components/layout.module.css
index 9924a88f..7e83794f 100644
--- a/packages/pharos-site/src/components/layout.module.css
+++ b/packages/pharos-site/src/components/layout.module.css
@@ -27,6 +27,7 @@ a {
 @media screen and (width <= 1055px) {
   .container {
     grid-template-areas:
+      'sidenav'
       'main'
       'footer';
     grid-template-columns: auto;
diff --git a/packages/pharos-site/src/components/layout.tsx b/packages/pharos-site/src/components/layout.tsx
index 7fbe612c..70403021 100644
--- a/packages/pharos-site/src/components/layout.tsx
+++ b/packages/pharos-site/src/components/layout.tsx
@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import type { FC, ReactElement } from 'react';
 import type { WindowLocation } from '@reach/router';
 import Sidenav from './Sidenav';
@@ -36,35 +36,70 @@ const Layout: FC<LayoutProps> = ({ children, location, fill }) => {
     typeof window !== `undefined` ? require('@ithaka/pharos/lib/react-components') : null;
 
   const [MainContent, setMainContent] = useState<ReactElement | null>(null);
+  const mobileBreakpoint = 1055;
+  const [isMobile, setIsMobile] = useState<boolean>(
+    typeof window !== `undefined` ? window.innerWidth < mobileBreakpoint : false
+  );
+  const [isSidenavDisplayed, setIsSidenavDisplayed] = useState<boolean>(!isMobile);
+  const containerRef = useRef<HTMLDivElement>(null);
 
   useEffect(() => {
-    const { PharosLink, PharosLayout } = Pharos;
+    const { PharosLink, PharosLayout, PharosButton } = Pharos;
+    const currentRef = containerRef.current;
+    const resizeObserver = new ResizeObserver(() => {
+      const windowWidth = window.innerWidth;
+      setIsSidenavDisplayed(windowWidth >= mobileBreakpoint);
+      setIsMobile(windowWidth < mobileBreakpoint);
+    });
 
     const body = (
-      <main className={main}>
-        <div className={topBar}>
-          <PharosLink id="skip-link" skip href="#sidenav-skip-link" isOnBackground>
-            Skip to main navigation
-          </PharosLink>
-        </div>
-        <PharosLayout
-          preset="1-col--sidenav-comfy"
-          className={`${content} ${fill ? content___fill : ''}`}
-          rowGap={fill ? PharosSpacing5X : '0'}
-        >
-          {fill ? children : <div className={page}>{children}</div>}
-        </PharosLayout>
-      </main>
+      <>
+        <Sidenav isOpen={isSidenavDisplayed} showCloseButton={isMobile} />
+        <main className={main}>
+          <div className={topBar}>
+            <PharosLink id="skip-link" skip href="#sidenav-skip-link" isOnBackground>
+              Skip to main navigation
+            </PharosLink>
+          </div>
+          <PharosLayout preset="1-col--sidenav-comfy" rowGap={fill ? PharosSpacing5X : '0'}>
+            <PharosButton
+              variant="subtle"
+              icon="menu"
+              data-sidenav-id="site-sidenav"
+              a11yLabel="Open side navigation"
+              style={{
+                display: isMobile ? 'block' : 'none',
+                paddingTop: 'var(--pharos-spacing-2-x)',
+              }}
+            />
+          </PharosLayout>
+          <PharosLayout
+            preset="1-col--sidenav-comfy"
+            className={`${content} ${fill ? content___fill : ''}`}
+            rowGap={fill ? PharosSpacing5X : '0'}
+          >
+            {fill ? children : <div className={page}>{children}</div>}
+          </PharosLayout>
+        </main>
+      </>
     );
 
     setMainContent(body);
-  }, [Pharos, children, fill]);
+
+    if (currentRef) {
+      resizeObserver.observe(currentRef);
+    }
+    return () => {
+      if (currentRef) {
+        resizeObserver.unobserve(currentRef);
+      }
+    };
+  }, [Pharos, children, fill, isMobile, isSidenavDisplayed]);
 
   return (
-    <div className={container}>
+    <div className={container} ref={containerRef}>
       <Fonts />
       <SEO title={pageName || 'Home'} pathname={location?.pathname} />
-      <Sidenav />
       {MainContent}
       <Footer />
     </div>
diff --git a/packages/pharos-site/src/components/variables.module.css b/packages/pharos-site/src/components/variables.module.css
index 8a400fc1..e3987326 100644
--- a/packages/pharos-site/src/components/variables.module.css
+++ b/packages/pharos-site/src/components/variables.module.css
@@ -16,3 +16,9 @@
   --sidebar-spacing-padding: var(--pharos-spacing-one-and-a-half-x);
   --main-spacing-padding: var(--pharos-spacing-7-x);
 }
+
+@media screen and (width <= 1055px) {
+  :root {
+    --main-spacing-padding: var(--pharos-spacing-2-x);
+  }
+}