In CSS, when we want to select an element based on its class attribute, we use the period symbol (.). This notation allows us to target all elements that belong to a specific class and apply styles to them accordingly.

For instance, if we have an HTML element like this:

<div class="example">This is an example.</div>

We can select this particular element using the following CSS:

.example {
    color: blue;
    font-size: 16px;
}

In this example, .example is the selector that targets any HTML element with the class "example", applying the specified styles.

Final Answer

The correct symbol to select an element with a specific class in CSS is: period (.).