I will try to explain, If I decide to use XenForo for my new site, I want to eventually edit templates and CSS. I'm just want to make sure I don't impede SEO or create any other negative effects. What should I look out for? Semantic HTML XenForo uses Semantic HTML, which is great! However, if one creates a customized skin then one will need to be careful what they edit. To my understanding its 100% safe to change the CSS, this will not effect the semantic markup what so ever? Editing the HTML can cause issues? What should I NOT touch? I'm assuming one should leave <header> <nav>, etc... alone? Anything else I should be cautious with?