   auto : left
        +
            0px : margin-left
        +
           35px : border-left-width
        +
            0px : padding-left
        +
           50px : width
        +
            0px : padding-right
        +
           15px : border-right-width
        +
            0px : margin-right
        +
            80% : right
        ====================
          500px : width of containing block (width of Initial Containing Block)

  becomes

        (solve) : left
        +
            0px : 