Adjusting width of prompt area.

IPython/frontend/html/notebook/static/css/notebook.css

@@ -183,7 +183,7 b' div.code_cell {'
 
 div.prompt {
     /* This needs to be wide enough for 3 digit prompt numbers: In[100]: */
-    width: 80px;
+    width: 11ex;
     /* This 0.4em is tuned to match the padding on the CodeMirror editor. */
     padding: 0.4em;
     margin: 0px;