The position CSS property sets how an element is positioned. By default during export elements are positioned absolutely using the top, right, bottom, or left properties and if selected transforms are used for centering.
You can change the layout position using the position dropdown.
Changing this option to anything but default or absolute can break your page from what it looks like on the artboard. If you know what you are doing this is desirable.
You can read more about these options in the position page: