Fix landing page for smaller screens

Summary:
Noticed things were starting to look crammed in smaller viewport, adding a bit of padding, and removing the 100% height which made the content of `main` overflow (and hence get cropped)

index.html

@@ -27,7 +27,7 @@
         margin: auto;
         flex-wrap: wrap;
         place-content: center;
-        height: 100%;
+        padding: 20px 0 20px;
       }
 
       a {