css reusability - http://cssguidelin.es/

css.reusability.css

/**
 * Runs the risk of becoming out of date; not very maintainable.
 */
.blue {
    color: blue;
}

/**
 * Depends on location in order to be rendered properly.
 */
.header span {
    color: blue;
}

/**
 * Too specific; limits our ability to reuse.
 */
.header-color {
    color: blue;
}

/**
 * Nicely abstracted, very portable, doesn’t risk becoming out of date.
 */
.highlight-color {
    color: blue;
}