Image too big in error message of checklist feature

When you are unable to save a checklist item, the red cross has a size too big 24x24.
When you save sucessfully a checklist item, the green mark size is 16x16.

The file "failed.png" with the red cross is used in other places, so the file should not be replaced.

To reproduce:

• Change the style of the span with the class saveChecklistError from "display:none" to "display:inline"