'Important' box wasn't terminated properly

Author: mr-c

src/topics/expressions.md

@@ -11,6 +11,7 @@ When manipulating file names, extensions, paths etc, consider whether one of the
 [built in `File` properties][file-prop] like `basename`, `nameroot`, `nameext`,
 etc, could be used instead.
 See the [list of best practices](best-practices.md).
+```
 
 ```{literalinclude} /_includes/cwl/expressions/expression.cwl
 :language: cwl