Make sure, you have added the below properties in your project.properties of your addon
<your>storefront.wro4jconfigscan.<your>addon=true
<your>addon.javascript.paths.responsive=/responsive/common/js/<your>addon.js;/responsive/common/js/<your>addon2.js
<your>aaddon.css.paths.responsive=/responsive/common/css/<your>addon.css;/responsive/common/css/<your>addon2.css
During the build, above js & css files will be added to your wro_addon.xml file under storefront resource folder.
Another way is to add your addon css/js path directly to ${ext.YOURstorefront.path}/wro_addons_template.xml
, which used to create wro_addon.xml
while building the platform.
Like
<groups xmlns="http://www.isdc.ro/wro" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.isdc.ro/wro wro.xsd">
<group name="addons_responsive">
<js>/_ui/addons/b2bacceleratoraddon/responsive/common/js/acc.checkoutsummary.js</js>
<js>/_ui/addons/customaddon/responsive/common/js/acc.customaddon.js</js>
<css>/_ui/addons/customaddon/responsive/common/css/customaddon.css</css>
</group>
</groups>