To add code to the snippet template, the following steps you need to follow :
Select the snippet and click on 
gear icon.
From the options, click on Edit Content. A new page titled “Snippet Template Information” will appear.
Click on the “Drop Image/Click Here 
button to select an image from your local device.. A snippet thumbnail image is a visual representation of a code snippet. It can be used to provide a visual representation of the code snippet.
In the code editor provided, enter the HTML and CSS code for your snippet.
To Upload an image, select “Images” from the dropdown menu and then click on the “Upload” button to select the image file from your local system. Once the image is uploaded, it can be used in the template by referencing the path of the uploaded image file.
If you need to upload a file or other asset that is not an image, choose “Other” from the dropdown menu and then use the “Upload” button to select the file from your local system. Once the file is uploaded, it can be referenced and used in the template just like any other asset.
Save the snippet by clicking on a button labelled “Update”.