Thank you for reaching out and thanks for using Callaway WordPress theme with BoldGrid Post and Page Builder. Sorry to hear you’re having having trouble adding custom CSS to your theme, but you are on the right track.
Try adding the bit of CSS to that same section to accomplish your task:
font-weight: 600 !important;
color: green !important;
Instead of bold we can use the font-weight attribute and set it 600;. We also used the !important tag so your new CSS overrides any global CSS classes.
I hope this helps! Please let us know if you have any other questions.