I think he's wrong here: requiring that folks preprocess some CSS-variant-with-constants into CSS-without-constants just multiplies the number of entities (by however many CSS variants are then introduced). CSS's lack of constants is a glaring design error.

If we want to reduce the total number of entities, then we should examine unifying HTML, CSS & scripting. As I've indicated elsewhere, I think that something like this would be awesome:

    ;; adapted from https://www.w3schools.com/howto/howto_css_modals.asp
    
    (html
     (head
      (title "modal-box-example")
      (style
        ;; The Modal (background)
       (.modal
        ;; Hidden by default
        (display none)
        ;; Stay in place
        (position fixed)
        ;; Sit on top
        (z-index 1)
        (left 0)
        (top 0)
        ;; Full width
        (width "100%")
        ;; Full height
        (height "100%")
        ;; Enable scroll if needed
        (overflow: auto)
        ;; Fallback color
        (background-color (rgb 0 0 0))
        ;; Black w/ opacity
        (background-color (rgba 0 0 0 0.4)))
    
       ;; Modal Content/Box
       (.modal-content
        (background-color #x"fefefe")
        ;; 15% from the top and centered
        (margin "15%" auto)
        (padding 20px)
        (border 1px solid #x"888")
        ;; Could be more or less, depending on screen size
        (width "80%"))
    
       ;; The Close Button
       (.close
        (color #aaa)
        (float right)
        (font-size 28px)
        (font-weight bold))
    
       ((.close:hover .close:focus)
        (color black)
        (text-decoration none)
        (cursor pointer)))
    
      (script
       (with-elements-by-id
        ((modal "myModal") (btn "myBtn")) document
        (let ((span (aref (get-elements-by-class-name document "close") 0)))
          (setf (on-click btn) (lambda () (setf (display (style modal)) "block"))
                (on-click span) (lambda () (setf (display (style modal)) "none"))
                (on-click window) (lambda (event)
                                    (declare (ignorable event))
                                    (setf (display (style modal)) "none")))))))
     (body
       ;; Trigger/Open The Modal
      ((button id "myBtn") "Open Modal")
    
      ;; The Modal
      ((div id "myModal" class "modal")
    
       ;; Modal content
       ((div class "modal-content")
        ((span class "close") ×)
        (p "Some text in the Modal..")))))