1. If you need to edit just the header, footer, pages, and products of your site and you don’t need to customize your site via customization then you don’t need the child theme. Because basically child theme is used for customization purposes. Like if you need to add a customization code you will use the child theme so that whenever you update the parent theme your customization will never be lost. But as you said you will not add any customization so you don’t need the child theme you can delete the child theme and use the parent theme.
2. Simply go to the Dashboard >> XSTORE >> Theme Options >> Theme Custom CSS there you will be adding the custom CSS code this option is coming from our theme see image for a better reference: https://postimg.cc/CZtj01tM and https://postimg.cc/RqwcrvT9
Regards 8Themes Team.
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