changing cell padding to match Jupyter Notebook.

src/notebook/theme.css

@@ -136,10 +136,10 @@
 
 
 .jp-Cell {
-  padding-top: 10px;
-  padding-bottom: 10px;
-  padding-left: 10px;
-  padding-right: 10px;
+  padding-top: 5px;
+  padding-bottom: 5px;
+  padding-left: 5px;
+  padding-right: 5px;
   border-width: 1px;
   border-style: solid;
   border-color: transparent;