Background image in html custom email does not work in shopify only

[Kromos]

Hello! 
I created an HTML email using a tool (external to shopify), a drag and drop builder which generates exportable html. In the email I generated there is a section with a background image and some text. When i see it in the external tool it works. It works also in the preview email I send myself from the tool. It works when I open it in my browser and so on. I mean that the image in the background is shown. 
When I copy the code in the shopify custom code section of the email tool it does not show. It does not show even when I send a test email.
I can't code but I understand the basics, can someone explain me why only the background image does not show? All images put there as img are ok, the background it the only problem.

[VIEKIN]

Hi,

The Shopify Email Template they have HTML special structure, if you not familiar with code also not know about structure of Email, you cannot customize that.

[Kromos]

Thank you, could you explain or give me a reference where I can understand in which way is the HTML of the Shopify Email Template special? I woluld like to understand at least.

[VIEKIN]

I think first you need backup an email template and save it to your local device. Then you also copy email template that and to a file Email-template.liquid to customize. Like this will easy to check and compare.