Suggestion: Add a w3- for dynamic font sizing to have max and min values based on the (s)mall (m)edium, and (l)arge that you have set for hiding and showing content in the grid. ex:
w3-large {font-size:18px!important}
@media (min-width:993px) {w3-large{font-size:13px!important;}}
@media (max-width:992px) and (min-width:601px) {font-size:w3-large{10px!important;}}
I would think a responsive font using the viewport setting would be ever better (or some combination):
w3-large {font-size:2vmax!important}
@media (min-width:993px) {w3-large{font-size:1.2vmax!important;}}
@media (max-width:992px) and (min-width:601px) {w3-large{font-size:10px!important;}}