Positive values move an element to the right and negative values move an element to the left.
The default value should be 0 if the left property is not used so the element is directly aligned with the left edge of the containing block. Remember that different browsers have different default values for different elements, so it is best not to assume anything. You can specify values for the left property in either absolute or relative units. A relative unit calculates the distance from the edge of the containing block using the width of the containing block. Some web browsers will skip the left property if the box has the default position value.