9. How do you change the background of an element in CSS?

This can be done using the background, background-color, background-image, background-repeat, background-position, and background-size properties.

/* Examples */
.element {
    background-color: lightblue; /* Changes background color */
}

.element {
    background-image: url('image.jpg'); /* Sets an image as the background */
    background-repeat: no-repeat; /* The image will not repeat */
    background-position: center; /* Centers the image in the element */
    background-size: cover; /* Scales the image to cover the element */
}