Merge branch 'class-add-remove-button' into 'dev'

Add add/remove class attr for button on multiple-f

See merge request documentation/doc!75

source/import_documentation/Mixins/widget-mixin.rst

@@ -210,14 +210,12 @@ Attributes
     - ``solid-form`` : all the resources of the container are displayed in a text widget.
     Buttons are automatically created to add and remove elements.
 
-    For ``solid-form`` only:
+    For ``solid-form`` only :
 
-    ``multiple-[field]-add-label``
-    ++++++++++++++++++++++++++++++
+- ``multiple-[field]-add-label`` : Text of the “+” button used to add an element  
 
-        Text of the “+” button used to add an element
-
-    ``multiple-[field]-remove-label``
-    +++++++++++++++++++++++++++++++++
+- ``multiple-[field]-remove-label`` : Text of the “x” button used to remove an element  
+    
+- ``multiple-[field]-add-class`` : Class of the “+” button used to add an element  
 
-        Text of the “x” button used to remove an element
+- ``multiple-[field]-remove-class`` : Class of the “x” button used to remove an element