SharePoint 2010 Hide Ribbon button using CSS

Steps

1. Use any Element inspector to find the id of the ribbon button. 
2. Use “\” backslash to escape period “.” 
3. Apply class in master page. 

Example

Before List Item Ribbon

• To Hide New List Item

#Ribbon\.ListItem\.New\.NewListItem-Large{Display:none;}

• To hide New item group. 

#Ribbon\.ListItem\.New.ms-cui-group{display:none;}

• To hide Delete button 

#Ribbon\.ListItem\.Manage-LargeMedium-1-2{Display:none;}

• To Hide List Manage Group

#Ribbon\.ListItem\.Manage { display:none; }