Dynamic Equations in MathJax

Expand the following: \begin{align} (x+1)^2 &\cssId{Step1}{= (x+1)(x+1)}\\ &\cssId{Step2}{= x(x+1) + 1(x+1)}\\ &\cssId{Step3}{= (x^2+x) + (x+1)}\\ &\cssId{Step4}{= x^2 + (x + x) + 1}\\ &\cssId{Step5}{= x^2+2x+1}\\ \end{align}