Called outer-container through "content" class in the header.

1. Removed unnecessary <div> in header.scss
2. Added the "content" class to the <div> in the header file.
Defined some footer and global classes for variables. Some colour changes header and footer background.
Styling the footer and combined the text into a single <p> tag.
Navigation link highlight updated

1. Defined class “highlight-text” to be used when nag links are
selected.
2. Changed the pixel values to em(pixel value), this is to convert the
pixel value to em.
Reverted back to the old <p> structure and changed property to "inline"
Added padding to the navigation links.
Merge branch 'main-layout'
Merge branch 'master' into index-page