Updated structure, added footer and css classes

src/components/Footer.js

@@ -0,0 +1,10 @@
+import React from 'react'
+import Link from 'gatsby-link'
+
+const Footer = () => (
+  <footer>
+    <h1>Footer</h1>
+  </footer>
+)
+
+export default Footer

src/components/header.js

@@ -2,17 +2,19 @@ import React from 'react'
 import Link from 'gatsby-link'
 
 const Header = ({ siteTitle }) => (
-  <h1 style={{ margin: 0 }}>
-    <Link
-      to="/"
-      style={{
-        color: 'white',
-        textDecoration: 'none',
-      }}
-    >
-      {siteTitle}
-    </Link>
-  </h1>
+  <header>
+    <h1 style={{ margin: 0 }}>
+      <Link
+        to="/"
+        style={{
+          color: 'white',
+          textDecoration: 'none',
+        }}
+      >
+        {siteTitle}
+      </Link>
+    </h1>
+  </header>
 )
 
 export default Header