Hi
It's declared in template style:
root/templates/ja_ego/scss/_styles.scss
you can find this declaration:
//
// MAIN BODY
// ------------------------------------
.t4-main-body {
padding-top: $grid-gutter-width;
padding-bottom: $grid-gutter-width;
If you're not familiar with SCSS, you can override by CSS in custom.css file of template.