<body class="home page page-id-2 page-template-default logged-in admin-bar customize-support" id="ls-global">
The body tag shown above has 7 classes and 1 ID. Which do you think would identify that page uniquely? It should be the ID. If other pages use that same ID (the name suggests that they could), then you will have to create a unique classname instead and add it to the list ("unique" meaning one that is not used on any other page). Uniqueness, one-of-a-kind, is the objective.
The correct way to list a unique group of classes in css is to separate them with dots. For example, the above body tag might be identifiable by listing several of its classes:
(Note the absence of spaces in the css address.)
This means that ALL of those classes must exist to target the tag that they belong to; in this case, the body tag.