1. Please activate child theme as per the below tutorial:
https://showthemes.zendesk.com/docs/khore/how-to-activate-a-child-theme/
Otherwise, you will lose the code changes when you upgrade the theme.
2. Then, navigate to Appearance->Editor->style.css
3. Add the below code to the end of the style-sheet:
@media (max-width: 767px) {
.video-card__title img { max-width: 70%; width: auto; }
}
4. Save the file.