How do you cancel/disable a CSS selector?

How do you cancel/disable a CSS selector?

References

Reference NO 1

http://stackoverflow.com/questions/13643371/how-do-you-cancel-disable-a-css-selector

Reference NO 2

http://stackoverflow.com/questions/3779534/how-to-disable-text-selection-with-css-or-js

Reference NO 3

http://perishablepress.com/css3-remove-box-shadow/

Reference NO 4

http://www.ozzu.com/website-design-forum/how-disable-css-for-one-link-t1287.html

Reference NO 5

http://unused-css.com/

Reference NO 6

http://dorward.me.uk/www/underline/

Reference NO 7

http://doctype.com/overwrite-css-rule-certain-class

Reference NO 8

http://www.pontikis.net/blog/remove-unused-css