homepage: Fix position of downward arrow to not overlap with text

Previously, the arrow overlapepd with the "Dotty Example Project" link in the Getting Started
section, making it difficult to click.

Author: smarter

docs/css/default.css

@@ -173,10 +173,6 @@ h1#dotty {
 div.centered-subtitle {
     text-align: center;
     font-family: 'Source Sans Pro', sans-serif;
-    position: absolute;
-    bottom: 0;
-    left: 0;
-    right: 0;
 }
 
 div.centered-subtitle > a {