Overriding existing CSS files

I want to use a css file for applying a theme. I am using myfaces that has one custom component named Schedul开发者_开发问答er. Scheduler component is using its own css file that is within jarfile(tomahawk12-1.1.10.jar) named schedule.css and has three theme(default , outlook, and evelutionary) but I want to use my own css file for applying theme in my project. How can I overwrite that css file?

Well it depends on if you want to completely overwrite the CSS files by changing their contents (just save over the files and possibly keep a backup copy), or if you want to just use the !important feature with your own custom stylesheet in CSS, exampled below:

leftSide {  
    background-color: #0f0 !important;  
} 

When the !important declaration is used on a specific property/value pair, it will cause that particular value to escape the cascade and become, as the name suggests, the most important value for that property, overriding any others. Here is more information on CSS's !important feature: http://www.impressivewebs.com/everything-you-need-to-know-about-the-important-css-declaration/