Mixed types: grid settings are integers, but `$max-width` is a string

[beep]

Since grid settings are all currently integers ($mar: 68; $col: 68; $gut: 26;), but $max-width is defined as a string (e.g., $max-width: 1680px;), it’s a bit tricky to do Sass calculations outside of josef.

For example, $mar / $max-width * 100% results in a Sass compilation error, as it’s asking Sass to divide 68 / 1680px. (Error: 4.04762%/px isn't a valid CSS value.) Manually converting $mar to a string does the trick, though:

( ( $mar + 0px ) / $max-width ) * 100%