UI changes in landing page

[AG-7219]

As per the figma design, the background of the landing page should be as follows:

Desktop View

Mobile view

While the site looks like this:

Desktop view

Mobile view

Clarify this with the design team and finalise the background image.

Also the navbar should highlight the currently active component (Noticeboard/timeline/contact page) as per the design but this has not been implemented. Should finalise this and implement if decided to integrate.