An important and useful feature of the SPAN tag is that it does nothing. Its only purpose is to surround other elements in your HTML code so that you can specify styles for them. .
The SPAN element was added to HTML to allow web page authors to provide styles without attaching them to an HTML structural element. SPAN is used as a selector in style sheets, and it also accepts STYLE, CLASS, and ID attributes.
SPAN is an inline element, so it can be used as elements in HTML such as EM and STRONG. The most important difference is that although EM and STRONG have structural meaning, SPAN has no such meaning. It exists purely to apply styles, so it has no effect when the style sheet is invalid.