Fixed canvas sizing bug

Changes

--- static/elements.css 8ca944c23103a6e3c873825623d3acf3b3a99af4

+++ static/elements.css 5dc4f7b6b60ae7b77cf16efeb6d4945ed28c67b4

@@ -65,6 +65,9 @@

+  box-sizing: border-box;

+  -moz-box-sizing: border-box;

+  -webkit-box-sizing: border-box;