When referring to a particular page on a large website, give the precise URL for that page. If the URL is so long that it causes a line break, you should try to break the line at a slash mark. Alternatively, if the website has a search facility, you might just give the URL of the home page.
(United Nations 1948)
United Nations (UN) (1948). Universal Declaration of Human Rights. http://www.un.org/en/universal-declaration-human-rights/index.html [2018-01-02]
Use (n.d.) in the date position for sources with no apparent date.
(University of Florida n.d.)
University of Florida (n.d.). History. http://www.ufl.edu/about/history/ [2018-03-02]