Font colour not displaying correctly

Hi,

I am trying to implement a button but for some reason the font colour differs on my website compared to what is displayed on the button output in the wordpress control panel.

The test page I have loaded the button on is https://www.energynerd.co.uk/japans-energy-costs-increase-as-yen-weakens/3066

The font should be in white. Is there anything I can try please?

https://www.ads-software.com/plugins/maxbuttons/