Class selectors

#1

html - >file

    <div class="item one"></div>

    <div class="item two"></div>

    <div class="item three"></div>

    <div class="item"></div>

</div>

css->file

div.item{
}

.item{
}

/*
so whats the difference between the ways and when i by mistake used
div.item{}
.one{}
to give styling and animation just the div.item worked in that case and not the .one{}
What was the problem?
*/