If a ‘background-image’ is specified, this property specifies the initial position on the Y-axis of the background image specified in the browser window if it is not continuously tiled in the element’s rendering box. A minimum value for this property indicates the upper side of the rendering box, and a maximum value is at the lower side. The X-axis component of the background position can be specified using the ‘background’, ‘background-position’ or ‘background-position-x’ properties.
[Percentage]: Percentage is in reference to the dimensions of the box of the current element. Value specifies the percentage on BOTH the image and the canvas and may be negative (eg: 70% indicates the reference point 70% from the top side of the image is to be located at 70% from the top side of the element’s rendering box.
[Length]: Represents an absolute Y-coordinate position for the image and may be negative. Standard Absolute or Relative Length Units may be used here.
tom|middle|bottom: Keywords representing Y-axis screen positions for image placement