JR Kanto area pass for travel in Yokohama?

Hi, I will be using the 3 day JR Kanto pass for travel from Tokyo to Yokohama for a day trip. Can I also use the pass for the JR lines within Yokohama or do I have to buy a Yokohama-Minatomirai Pass separately?
Thanks.

Hi, I am interested to know more on the pass. Would it be cheaper if travel direct from Narita to Yokohama staying for 1-2 days then go to Tokyo?

@JT71 : Yes, all the lines between stations in Yokohama are inside the coverage area of the Kanto Area Pass. If you are looking at the diagram on the JR East webpage, not all stations are indicated there (probably because there would be too many), but if a segment is in blue, all stations on that segment are fine.

A 3-day Kanto Pass is Y8000. That is Y2666 per day. It will be very difficult to spend even 1/2 that amount on trains around Yokohama.
Tokyo to Yokohama on a JR train is only Y450 and less than that on a Keikyu or Tokyu private railway train.
It's only a few kilometers and about a 25 minute ride.

JR Kanto area pass pays off only with at least a trip to Fuji lakes area, Nikko, Izu Peninsula or similar long distace trip.

Can I also use the pass for the JR lines within Yokohama?

Yes; but a JR Kanto Area Pass does not easily pay off with such short trips.

Major tourist spots in Yokohama City are not concentrated in one or two areas but located in several areas; some of them are a bit apart from railroad stations.

If you hope to visit several tourist spots in Yokohama time-efficiently, Akai Kutsu Bus may be good as a transportation mode. It has two lines (Line C and Line M) and its regular fare is 100 yen per adult per ride. Its possible demerit is that its routes are partly complicated.
http://www.yokohama-bus.jp/akaikutsu/en/index.html

do I have to buy a Yokohama-Minatomirai Pass separately?

Well, this pass can be cost-effective if you visit spots near some stations inside the valid area; but please note
that this pass does not cover rides between stations in Tokyo and stations in Yokohama
and that in Yokohama Station(s), the JR platforms are on the 1st floor (= the ground floor) while the platform of Minatomirai and Tokyu is deep under the ground on the 5th basement.

If you start from a station of Tokyo Metro subway Hibiya Line or Tokyu Toyoko Line in Tokyo, a Tokyu Minatomirai Ticket may be a good choice. It covers also one roundtrip rides on Tokyu Toyoko Line, not only rides on Minatomirai Line; you do not have to change platforms in Yokohama.
http://www.tokyu.co.jp/railway/railway_global/english/otoku/mm_ticket....

You can take an Akai Kutsu bus from Bus Stop No. 4 in the bus terminal near Sakuragicho Station of JR-East.