Jose Mortellaro

It adds CSS selectors in the HTML where there are not.
Sometimes you need some custom CSS and you realise a specific element of the DOM is without any selector. 
After activating this plugin you will not have anymore this problem. Every element of the DOM will have a class name that begins with css-sel-. 
There are no options, just activate the plugin.
To see if it works, in the frontend right-click with your mouse and click on “Inspect” (usually F12). Then you should not see any more DOM elements without any class.
The only elements that may still miss a CSS class are those ones that are added dynamically through JavaScript. In this last case the plugin can’t do anything, because it works only on the server before sending the page to the browser.
It adds no HTTP requests, and no queries to the database.
<h3>Help</h3>
If you need help open a thread on the support forum of this plugin. 
Please, before posting enable the debugging in wp-config.php. Need a step-by-step guide? Read <a href="https://freesoul-deactivate-plugins.com/how-to-enable-debugging-in-wordpress-a-step-by-step-guide/" rel="nofollow ugc">this detailed tutorial</a> on <a href="https://freesoul-deactivate-plugins.com/how-to-enable-debugging-in-wordpress-a-step-by-step-guide/" rel="nofollow ugc">how to enable debugging in WordPress</a> to learn more.

CSS Selectors

It adds CSS selectors in the HTML where there are not.

onigoetz

This plugin uses the eCSStender javascript Library. This library is a parser that takes your CSS after the browser.
The library re-interprets the css using the plugins and adds new abilities to the browsers. You can for example add CSS3 Selectors support to IE6.
It will be less a Pain to develop a theme for IE6 or other browsers now.

eCSStender

Extend the functionalities of CSS by adding plugins to eCSStender

CSS Selectors vs eCSStender