You can use the click
event on #cboxClose
this way to redirect to your main page:
$("#cboxClose").click(function(){
location.href = "main-page.html";
});
Applying changes to the code:
$(document).ready(function(){
$.colorbox({width:"60%", inline:true, href:"#suscripcion", transition:"fade"});
$("#cboxClose").click(function(){
location.href = "main-page.html";
});
});