How to remove space before and after featured image in mobile

I am now using 1200 px x 800px feature image size but the problem of white space under featured image persists on mobile

Hello @afroimmersive

You can use the following code in additional CSS box in customizer:
@media(max-width:767px) {
.single-post .entry-thumbnail .post-thumb {
height: auto;
}
.single-post .site-content {
margin-top: 0;
}
}

Thanks ??

Thank you. This worked perfectly