Inequality $||\theta_x||_{L^{\infty}}+||\mathcal{H}\theta_x||_{L^{\infty}}\leq C ||\theta||_{H^{2}}$

Question

If $\mathcal{H}$ denotes Hilbert transform and $\theta\in H^{2}$ classical Sobolev space. How to prove that there is $C>0$ such that $$||\theta_x||_{L^{\infty}}+||\mathcal{H}\theta_x||_{L^{\infty}}\leq C ||\theta||_{H^{2}}.$$