you are using the default demo template - classic.
It is not wise to use it directly for your add on and modifications, it will be over wirte in the future upgrade. And you will create more troubles in upgrading.
Suggest to use your own template for that and it is easy.
My steps,
1. copy the classic template directory to a new template directory, called
includes/templates/classic_my
2. and modify the file, in your new template, for your own use
includes/templates/classic_1/template_info.php
Code:
$template_name = 'Classic Contemporary Green';
3. For example, to read as
Code:
$template_name = 'My Classic Contemporary Green';
It is only for example, you can change it to whatever you like.
And it will show up in the admin's Template Selection as a new template's title for selection.
Then within a minute or two, after the above steps, you can clone a template for your own use. It will not be overwrited in the upgrade.
And you have a new template and the path is:
includes/templates/classic_my