Update custom.scss

Fix white footer's background being visible on the sidebar when using fixed footer layout. I fixed by putting the page footer padding equal to the sidebar footer padding.

src/scss/custom.scss

@@ -693,7 +693,7 @@ a:hover, a:focus {
 }
 footer {
   background: #fff;
-  padding: 15px 20px;
+  padding: 10px 20px;
   display: block;
 }