How do you apply multiple classes to an HTML element?

The correct method to apply multiple classes to an HTML element is by listing them separated by spaces within the class attribute. This approach helps to combine the styling and behaviors defined in different classes, allowing for more versatile and modular code.

When multiple classes are used, the styles from each class are merged, and if there are any conflicts, the styles defined in the last class in the list take precedence. For instance, if you have classes defined as .class1 { color: blue; } and .class2 { color: red; }, applying both classes to an element like this: <div class="class1 class2"></div>, will result in the text color being red, due to the cascade nature of CSS.

Using commas, a plus sign, or nesting classes does not conform to standard HTML practices for class assignment and will not yield any valid results in applying multiple styles. Therefore, the method of spacing is the only correct approach for achieving the desired outcome.