code: function (fontSize, elem) {
              fontSize = fontSize || this.style.fontSize;
              if (elem && win.getComputedStyle) {
                  elem = elem.element || elem; // SVGElement
                  fontSize = win.getComputedStyle(elem, "").fontSize;
              }
              fontSize = /px/.test(fontSize) ? pInt(fontSize) : /em/.test(fontSize) ? parseFloat(fontSize) * 12 : 12;
  
              // Empirical values found by comparing font size and bounding box height.
              // Applies to the default font family. http://jsfiddle.net/highcharts/7xvn7/
              var lineHeight = fontSize < 24 ? fontSize + 4 : mathRound(fontSize * 1.2),
                baseline = mathRound(lineHeight * 0.8);
  
              return {
                  h: lineHeight,
                  b: baseline,
                  f: fontSize
              };
          }
docs: Utility to return the baseline offset and total line height from the font size