Step 1: Customize the button(s) as you wish, then copy the code (in this example we only add the Invoice button):



Step 2: On Shopify Admin, go to Settings -> Checkout, look for Additional Script box under Order Processing, then paste the code:



- Step 3: Replace the first line, from:


<div style="margin-top: 10px; display: flex; justify-content: center; flex-direction: row">


to:


<div style="margin-top: 10px; display: flex; justify-content: center; flex-direction: row;position: absolute;bottom: 0;left: 0;">


and add this line of code at the bottom:


<style type="text/css">

    

    .step {

        position: relative;

        padding-bottom: 60px;

    }

</style>


It should look like this:



- Step 4: Save and check on Front-end: