use semantic main element instead of a div

static/build.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/build"/>
         <script type="module" src="/redirect.js?6"></script>
@@ -39,7 +39,7 @@
                 <li><a href="/contact">Contact</a></li>
             </ul>
         </nav>
-        <div id="content">
+        <main>
             <h1 id="build">
                 <a href="#build">Build</a>
             </h1>
@@ -1220,7 +1220,7 @@ rm android-cts-media-1.5.zip</pre>
             if it truly makes the correct approach simpler. Ignore fads and figure out if it
             actually makes sense to use, otherwise just stick to the old fashioned way if the
             fancy alternatives aren't genuinely better.</p>
-        </div>
+        </main>
         <footer>
             <a href="/"><img src="/logo.png" width="512" height="512" alt=""/>GrapheneOS</a>
             <ul id="social">