Hello,
To change when the module collapses all the sections into one single column you would need to edit the CSS here:
modules\mod_s5_horizontal_accordion\css\s5_horizontal_accordion2.css
Notice:
@media screen and (max-width: 700px){
.horzaccordion {
height:auto !important;}
.horzaccordion li {
float: none !important;
width: 100% !important;}
}
This is what sets when the columns collapse into one.