/* 2 separate classes - yes space */
.classOne .classTwo {
color: red;
}

/* multiple classes - no space */
.classOne.classTwo {
color: lime;
}

/* id and class - yes space */
#myid .myclass {
border-top: 0px;
}

/* id with class - no space */
#myid.myclass {
border-top: 0px;
}