how does additional css rendering work?

Additional CSS in the customiser is core WordPress functionality and shouldn’t behave differently between themes. You can see in /wp-includes/js/customize-preview.js that the preview is simply JavaScript that simply sets the content of the <style id=”wp-custom-css”></style> element to the content of the Custom CSS text field. The <style> element itself is added by the wp_custom_css_cb() function … Read more

How to display javascript banner in website header?

It’s there and visible in Incognito mode, it’s being blocked by one of the adBlocker extension that you might be using in your browser. The best workaround would be is to change the class from headad to something more generic like head-banner. Make sure you update the style in your theme/plugin. Banner with updated class:

Unable to properly load WordPress Admin page

Looks like theme problems to me. I’d change it back to one of the ‘Twenty’ themes as a first step. If OK, then start diagnosing the theme. (You could reinstall the theme manually which might protect settings, or FTP the theme files manually. Or just remove the theme and reinstall, but you might have to … Read more

Page flickers when new html5 video loads

Does this all videos have the same height and width? I have just added a height for the video tag and the flickering issue is solved. You can either use a static height or use jquery to add height dynamically at page load.