[SOLVED] Classes added to style.css seem to be ignored

For some content I like to use my own ccustom table style and thus I added a class (derived from table) to the 'styles.css' file like;

table.mytable {
border-width: 0px;
border-spacing: 0px;
border-style: none;
border-color: gray;
border-collapse: collapse;
background-color: white;

However, when I apply the class in my content (using html edit) it is completely ignored. Is this by design or am I making a mistake?