ifyComputedStyle("background-size", "calc(67% - 54% + 4em) 50%", "calc(13% + 64px) 50%");

    /*
    "Where percentages are not resolved at computed-value time,
    they are not resolved in math functions (...)"
    https://www.w3.org/TR/css-values-4/#calc-serialize

    Therefore here, the percentage is preserved and
    a calc() wrapper must be used. The 4em term
    must be resolved though.
    */

    verifyComputedStyle("background-position", "calc(100% - 100% + 20em)", "calc(0% + 320px) 50%");

    /