Size (fontSize)
The Size property sets the font size in points for a node and for all children of the node.
During expression evaluation the variable fontSize is available, which contains the inherited font size. This variable can be used for relative font sizing. For example, the expression fontSize="fontSize*1.2" makes the current font 20% larger than the parent font.
Type: Numeric.
The default value (not the expression) is inherited from the parent. The font size of the root node is 12 point.
You can find the Size property in the Font category of the Properties view.