Change CSS rule at runtime

Question

How do I change any CSS properties during runtime?
Suppose I have:

#mycss {
   background:#000;
   padding:0;
}

Then during runtime,

Answer 1

There are multiple ways css rules can be overridden:

• Any element will take on the css rule defined nearest to the bottom of the css document you include.
• Any inline style will override the css rule defined in the css document.
• Any javascript has the ability to dynamically adjust the css properties of any given element.
• Any element can take on the property of !important, which defeats anything else defined.