If you want to have a simple website without tabs, simply create all content in the header and delete the contents for all tabs. This way no tabs are displayed and the website is one flat page.
The best designs are often very simple: match the colors well together, position your texts so that they can be read without scrolling and don't over use pictures
If you only perform one event, you should consider switching off the navigation (Navbar + Sidebar) so that the participants do not get confused by the options and are completely focused on your page. Remember to add a logout merge tag so that the participant can log out.
You can count on the fact that some of your participants do not want to read long texts, but only want to make a quick statement. Therefore, position the login button as best as possible on the first page.
If possible, renounce texts to images. Due to the responsive design, large images are always adapted to screen widths. If you look at the event website on a smartphone, the text in a picture becomes very small and possibly barely readable.
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