I thought this was a good idea, so I added a BlockQuote style to the custom stylesheet I normally use. That is, I added the cell
Cell[StyleData["BlockQuote"],
CellMargins->{{90, 3.}, {4., 4.}},
MenuSortingValue->1540]
You can do the same.
If you don't already have a custom stylesheet, do the following:
- Open any new notebook in the default style.
- Choose Edit Stylesheet... from the Format menu.
- Type BlockQuote into the input field at the top of the stylesheet template. Hit Return.
- Select the BlockQuote cell that appears and type Cmd+Shift+E
- Select the
Cell
expression and paste the above code over it.
- type Cmd+Shift+E
- I didn't want a background color so I didn't set one. You can set one at this point by selecting the BlockQuote cell and giving it a background color using the Format menu.
- Click on the Install Stylesheet... button at top-right of the stylesheet template and install the new stylesheet.
Update
This update addresses a further question asked by the OP in a comment below.
The easiest way, I think, is to open a new notebook, give it your custom stylesheet as its stylesheet, choose Edit Stylesheet... from the Format menu, make your edits and then reinstall the stylesheet.
The installation dialog will insist that you give the edited stylesheet a name different from its current name. For how to deal with that read the notes to this answer