CSS multiple selectors without comma

itemprop="text">

I am alittle confuse about CSS
Selectors, I understand that we can group multiple css selectors with a comma if they
share similar attributes, but what about multiple css selectors without commas e.g like
this:

.ui-datepicker-rtl {
            direction: rtl; }
.ui-datepicker-rtl .ui-datepicker-prev { right: 2px; left:
            auto; }
.ui-datepicker-rtl .ui-datepicker-next { left: 2px; right: auto;
            }

itemprop="text">

class="normal">Answer

When you
use the comma,
like

#menu,
            .item

you are saying:

all elements
whose id is menu AND all elements whose class is
item

When
you nest selectors without the comma, like

#menu
            .item

you are saying

all elements that
has class item inside a container whose id is
menu