Hi Hennie,
It’s a trial and error, try the first one and if it’s not working then add !important too. And about styling for different sizes, yes, you could do it, example,
@media screen and (min-width: 980px){
.title-about{
font-size: 16px !important;
}
}
@media screen and (max-width: 979px){
.title-about{
font-size: 13px !important;
}
}
@media screen and (max-width: 767px){
.title-about{
font-size: 10px !important;
}
}
Now, that’s responsive since you use multiple @media with different styling values. And again, it can be with !important or without it, use the one that will work. There is no way you can predict when !important should be used since Wordpress has themes and plugins from different authors and they loaded their own CSS with different priorities, it’s a trial and error 
Thanks!