Yes you can apply more than one class to a div but only if the 2 classes have different style properties.
in your code, for example
.one .two {
font-size:32px;
color:red;
}
Means that you want two classes with the same formatting (not sure why as classes can be re-used as many times as you like in a page unless each class has other styling separately within your CSS) and you are then applying both to your html which is completely unnecessary, however
.one {
font-size:32px;
color:red;
}
.two {
font-weight: bold;
}
Means you are setting two different classes which have different properties and then you may need to apply both to your span as you have done.