Add the following CSS to design customizations:
.page-preview-item, .page-title {
max-width: 1000px;
padding-left: 10px;
padding-right: 10px;
}
To apply it only on mobile use media queries. In the following example it will apply only for screens with the width less than 760px:
@media and (max-width: 760px) {
.page-preview-item, .page-title {
max-width: 1000px;
padding-left: 10px;
padding-right: 10px;
}
}