SideBar visibility and MobileNav close button

[Temi-Tade]

• On the landing page, the SideBar component is visible when the user is not signed in. On mobile, the hamburger menu icon that opens the MobileNav is also visible. I can use the useUser hook from clerk to get the isSignedIn status and toggle the sidebar and hamburger menu accordingly.

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• Also, the colour contrast between the close button (x) in the MobileNav and the background is poor, I will change this for better visibility for mobile.

[github-actions]

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