Divisions or as they're commonly called div's are probably the most frequently used element. Div's are how we create all the different sections of a webpage. A div exist by itself or as a container for other elements. The color of a div can be set using the background property. You can also add a border around the div using the border property. To add a border you need to define the border's size, style(solid), and color. By default there is no background or border for a div, so you have to enter it. Playing around with changing the width, height, background and border.
Notice you had the option to set the width of the div in px or %, but for height you only had the option of px. Actually, you can set the height of a div in % as well, but its more complicated and not worth covering now. Here, the border style is set to solid. You can also set it to dotted or dashed, but it rarely looks good so its not used often. If you don't want the div to have a background you can set it to none.