use semantic main element instead of a div

static/source.html

@@ -20,7 +20,7 @@
         <meta property="og:site_name" content="GrapheneOS"/>
         <link rel="icon" type="image/vnd.microsoft.icon" href="/favicon.ico"/>
         <link rel="mask-icon" href="/mask-icon.svg" color="#1a1a1a"/>
-        <link rel="stylesheet" href="/grapheneos.css?18"/>
+        <link rel="stylesheet" href="/grapheneos.css?19"/>
         <link rel="manifest" href="/manifest.webmanifest"/>
         <link rel="canonical" href="https://grapheneos.org/source"/>
     </head>
@@ -38,7 +38,7 @@
                 <li><a href="/contact">Contact</a></li>
             </ul>
         </nav>
-        <div id="content">
+        <main>
             <h1 id="source">
                 <a href="#source">Source</a>
             </h1>
@@ -74,7 +74,7 @@
             for the Auditor and AttestationServer sources. The latest release of the Auditor app
             is included in the GrapheneOS source tree as a prebuilt since it uses a different
             build system, similar to other prebuilts like Chromium.</p>
-        </div>
+        </main>
         <footer>
             <a href="/"><img src="/logo.png" width="512" height="512" alt=""/>GrapheneOS</a>
             <ul id="social">