Question - What is cascade?
Answer -
Cascade is a method of defining the weight (importance) of individual styling rules thus allowing conflicting rules to be sorted out should such rules apply to the same selector.
Declarations with increased weight take precedence over declaration with normal weight:
P {color: white ! important} /* increased weight */
P (color: black} /* normal weight */
Are Style Sheets case sensitive?
No. Style sheets are case insensitive. Whatever is case insensitive in HTML is also case insensitive in CSS. However, parts that are not under control of CSS like font family names and URLs can be case sensitive - IMAGE.gif and image.gif is not the same file.