In CSS remember that font family names and URLs can be case sensitive, but so far I never tried differentiating two CSS class names by different case (upper and lower), hence never got to deal with case sensitivity of CSS, but on of my friends got this question in an interview, later figured out, but default CSS is not case sensitive, but XML or XHTML DOCTYPE declaration can make CSS class names case sensitive.
Always we should follow standards, but it’s good to know sub-standard implications as well. because you don’t know, some day you might end up using code written by other programmers.
So next time when some body ask you about case sensitivity of CSS, blame DOCTYPEs.
Asv3's Blog 