Strong font does not show

Hello, I have your theme installed here: https://z99.ch/ However, the text marked with the strong tag does not show. I have attempted to change the weight via the Customizer and CSS file. You can see for yourself on this screengrab: http://z99.ch/wp-content/uploads/2017/07/Screen-Shot-2017-07-11-at-6.47.05-PM.png Please advise, LF