Type
baseline to align the element's baseline with the parent's baseline.
Or type
middle to align the middle of the element with the middle of the parent.
Or type
sub to position the element as a subscript of the parent.
Or type
super to position the element as a superscript of the parent.
Or type
text-top to align the top of the element with the top of the parent.
Or type
text-bottom to align the bottom of the element with the bottom of the parent.
Or type
top to align the top of the element with the top of the tallest element on the line.
Or type
bottom to align the bottom of the element to the bottom of the lowest element on the line.
Or type a percentage of the line height of the element, which may be positive or negative.