you can try adding it to theme.liquid
Follow this:
Go to Online Store->Theme->Edit code->theme.liquid-> tag->paste bellow code in bottom of file
@media not all and (min-resolution:.001dpcm)
{ @supports (-webkit-appearance:none) {
@media (max-width:767px){ .collection-item__title {
font-size: 12px !important;
}
}
}}