hiratatsuya

CSS and JS Enqueuer plugin will enable to enqueue external CSS and JS, and edit it. 
You can customize the web site at only the dashboard.

CSS and JS Enqueuer

CSS and JS Enqueuer plugin will enable to enqueue  external CSS and JS, and edit it.

cyberduck

Looking for a fast and easy way to add custom buttons to the WordPress Visual Editor? Look no further. With this plugin you can easily add your own custom buttons in the Visual Editor, as well as the HTML Editor. You can then add HTML code to the button, either as a wrap (before, after) or as a single block. On top of that you can, from within the plugin, set the CSS so you can view the effect of the button directly in the Visual Editor.
The plugin comes with a large number of ready to use button icons, but you can also add your own.
Visual Editor Custom Buttons. The perfect plugin for customizing the Visual Editor, add special features and simplify the content update process for the novice user.

Visual Editor Custom Buttons

This just works, simple and elegant. Create an editor toolbar button and define what it should insert in html.

Excellent tool for customizations in the editor

Visual Editor Custom Buttons lets you add custom buttons to the Wordpress Visual Editor.

CSS and JS Enqueuer vs Visual Editor Custom Buttons