Gagan Goraya

This is a very slim piece of plugin that gives you incredible flexibility to apply your own CSS class(s) to any specific widget.
If this plugin is activated, it will present an additional ‘CSS Class’ field in every widget.
You can input any css class name or even more than one class name by separating each with a space.
If, somehow your widget is not wrapped inside an HTML block element (depends upon the theme you are
using), this plugin will intelligently wrap the widget with a DIV tag and apply to class to it.

Simple CSS for widgets

This plugin lets you specify CSS class(s) for widgets to apply your own CSS definitions to specific widgets.

Aiken1

Simple plugin that adds extra functionality to menu items. The plugin will allow to set predefined CSS classes (Select field) to menu items. 
Support for the plugin “If Menu”: https://wordpress.org/plugins/if-menu/ – does not break the “If Menu” plugin.
Example of defining CSS classes for menu items is in the “FAQ” tab here.
Custom Menu Class is 100% free. if you have questions or need additional information u can comment on my website ( http://deving.de – http://deving.de/blog/wordpress/2292-wordpress-plugin-fuer-voreingestellte-css-klassen-fuer-menue-links/ ) or in the “Support” tab here.
Check out my <a href="http://themeforest.net/user/Aiken1/portfolio?ref=Aiken1" title="Themeforest" rel="nofollow ugc">Themeforest Account</a>

Simple CSS for widgets vs Custom Menu Class