Shopify checkout page custom changes possible?

Question

If I remove existing checkout design code and put there own designed (HTML, CSS) code... then where I can submit the form data and which parameters will be required for form data submission..?

I changed this below code with my HTML code, so the design that I was expecting is done now, the next step is to data store in shopify DB. So what will be the form action ? and what will be the handles ? and what will be the layout effects ?

<div class="content" data-content>
      <div class="wrap">        
        <div class="main" role="main">
          <div class="main__header">
            {{ content_for_logo }}
            {{ breadcrumb }}
            {{ alternative_payment_methods }}
          </div>          
           
          <div class="main__content">                 
            {{ content_for_layout }}
          </div>
          <div class="main__footer">            
            {{ content_for_footer }}           
          </div>
        </div>
        <div class="sidebar" role="complementary">
          <div class="sidebar__header">
            {{ content_for_logo }}
          </div>
          <div class="sidebar__content">
            {{ content_for_order_summary }}
          </div>
        </div>
      </div>
    </div>

Answer 1

You cannot alter Shopify checkout with your own code unless you are paying rent on a Plus plan. With a Plus plan you can alter checkout in some respects as you get access to checkout.liquid.

If you are on Plus, take a look at their form elements and see if you can make sense out of altering them.