add visuals: code demo, buttons, preview image

Author: tiye

assets/main.css

@@ -73,17 +73,3 @@ body * {
 .md-block .md-p a {
  white-space: pre;
 }
-
-.main-title {
-  font-size: 40px;
-  line-height: 48px;
-  font-weight: bold;
-  font-family: Federo, cursive;
-}
-
-.secondary-title {
-  font-size: 24px;
-  line-height: 30px;
-  font-weight: 500;
-  /*font-family: Federo, cursive;*/
-}