How can we specify all the background styles in one declaration?

By using the background (shorthand) property.

The background shorthand CSS property sets all background style properties at once, such as color, image, origin and size, or repeat method.

This property is a shorthand for the following CSS properties (is recommended order):

• background-image
• background-position
• background-size
• background-repeat
• background-attachment
• background-origin
• background-clip
• background-color

body {
  background:
     url(sweettexture.jpg)    /* image */
     top center / 200px 200px /* position / size */
     no-repeat                /* repeat */
     fixed                    /* attachment */
     padding-box              /* origin */
     content-box              /* clip */
     red;                     /* color */
}