MLA = Modern Language Association
Usually, you can use the style for citing a print book and then just add the additional information to indicate its electronic origin and when you accessed it, as shown below.
The point to remember is to include enough information for others to be able to find your source.
Book available only on the web or downloaded to an e-device
Book that has been scanned and put on the web (e.g., from Google Books or from The Complete Works of Charles Darwin Online)
See also the online example from the source below:
APA = American Psychological Association
Note that APA style requires you to add the type of e-device, where you retrieved the e-book, and the URL or doi.
Search the APA Style Blog, for more information about citing electronic things.