Bedford: Can I set a maximum site width?

Yes, if you are using a Bedford-family template and want to limit the site width and have borders down the left and right sides, you can add this to Custom CSS:

body {
    max-width: 1110px;
    margin: 0 auto;
    background-color: aliceblue;
}

Where max-width is the maximum width you require, and background-color will set the colour of the left and right borders.