Its CSS's rule that you can't use Number as starting character or a class or id. That is why it wont work. You at least have to put 1 alphabet before the number!
This is what said in w3c -
In CSS, identifiers (including element names, classes, and IDs in selectors) can contain only the characters [a-zA-Z0-9] and ISO 10646 characters U+00A0 and higher, plus the hyphen (-) and the underscore (_); they cannot start with a digit, two hyphens, or a hyphen followed by a digit. Identifiers can also contain escaped characters and any ISO 10646 character as a numeric code (see next item). For instance, the identifier “B&W?” may be written as “B\&W\?” or “B\26 W\3F”.
http://www.w3.org/TR/CSS21/syndata.html#characters