Solved Sticky header

It's a bit tricky to achieve that. Try the below:

Step 1:
Add free-sticky CSS Class to the top section.

Step 2:
Change the 121px to your top section height. As for the 153px, change it to your top section height + 32px.

Code:

.free-du-plugin-header .free-sticky-wrapper .et_section_regular:not(.et_pb_fullwidth_section) {
    position: fixed!important;
    width: 100%!important;
    height: 121px!important;
}
.free-du-plugin-header .free-sticky-wrapper .et_pb_fullwidth_section {
    position: fixed!important;
    width: 100%!important;
    top: 121px!important;
}
.admin-bar .free-du-plugin-header .free-sticky-wrapper .et_pb_fullwidth_section {
    top: 153px!important;
}

It should work then.