Hi,

This is the example code of breakpoint of this theme, please customize as you want and go to Appearance > Customize > Additional CSS, then paste:

/* Large Desktop */
@media screen and (min-width: 1440px) {
    .penci-container-fluid, .two-sidebar .site-main .penci-container {
        max-width: 1430px;
    }
}
/* Tablet Horizontal */
@media screen and (min-width: 1241px) {
    .penci-container, .penci-container-fluid {
        width: 100%;
        max-width: 100%;
    }
}
/* Tablet Vertical */
@media screen and (min-width: 960px) and (max-width: 1240px) {
    .penci-container-fluid, .penci-container.penci-vc_two-sidebar, .two-sidebar .site-main .penci-container {
        width: 100%;
        max-width: 100%;
    }
}
/* Mobile */
@media screen and (max-width: 768px) {
    .penci-container, .penci-container-fluid {
        padding-left: 0;
        padding-right: 0;
    }
}