You have the class & id markers switched around. # = id, . = class. Also, you have two selectors that belong to different elements concatenated, which is the way to indicate that they both apply to the same element. They need to have a space between them (and be given in the exact order shown) to indicate that #categoriesHeading is inside .leftboxcontainer. Finally, #categoriesHeading is plenty specific to control the heading; you don't need .leftboxcontainer.
Code:.leftboxcontainer #categoriesHeading { display:none; } /*or just this*/ #categoriesHeading { display:none; }




