Changing the default style of an HTML element, can be done with the style attribute.
The HTML style attribute has the following syntax:

<ANYTAGNAME style="property:value"> </ANYTAGNAME>

Tip:

This is an example of inline-style.
But use CSS styling with classes nowdays!

HTML code:

<ANYTAGNAME class="backgroundRed"> </ANYTAGNAME>

CSS classes:
.backgroundRed {
    background-color: red;
}