Family Search example of citing sources gives this as an example.
“Idaho Marriages, 1842-1996,” Ancestry.com (https://www.ancestry.com : accessed 18 July 2010), search for Alonzo Raymond, married 1922; from “Upper Snake River Family History Center and Ricks College (Rexburg, Idaho),” citing “marriage book at the County Courthouse located in Bannock Co., ID in Volume 11 on Page 55.”
Let's break down the example: In "Evidence Explained" by Elizabeth Shown Mills (citation for this book is on the Family Search example page), she says that online sources should be cited as if they were books. I've included a couple of updated changes.
1. The collection name, "Idaho Marriages, 1842-1996," and then where it was found -- at Ancestry.com with your access date.
2. You need to include the information about why you were there: "Search for Alonzo Raymond," give the marriage date and who he married and where. (The example only provides the marriage date.)
3. Where did the information come from? Cite that: Upper Snake River Family History Center and Ricks College (Rexburg, Idaho)"
4. Where Ancestry.com got the information: "marriage book at the Bannock County, Idaho courthouse. Volume X, page #, certificate number if used. (The example does not include the certificate number which may/ or may not be used in your case.)
And #5 , this is not included in the example:
5. I would include the url where you are. First copy the url code when you are looking at the image. Second: place that url in [ brackets ] but before you're done -- give it a name like Idaho marriage -- so it looks like this [https://ancestry.com/ blah blah blah...../.... Idaho marriage] There is one space between the end of the url and your name of the document. Then, someone with an ancestry.com subscription will be able to go to your link. Without the subscription, they will be re-directed to the Ancestry.com homepage.
It's true this is a great deal more work than putting Ancestry. It would be lovely if they provided the great citation for the document and the image that Family Search does.