Custom modeBarButton - icon renders fine everywhere...except the plotly modeBar

I want to replace the Download image icon in the modeBar - seems like a simple enough task?
It's been a real struggle though.
I have this icon:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="-8.717 -10 17.435 20" width="17.435" height="20"><path stroke="#666" fill="none" d="m-4.048-.989 3.992 3.667L4.065-.908M-4.064 2.37v2.336h7.982V2.369m-3.992.244v-7.319" stroke-width="1.176"/></svg>

I'd like to use it as the Download image icon, based on a bunch of research on SO, Plotly issues and posit community forums I've come up with the following code for doing so:

dl_button <- list(
  name = "Save As Image",
  icon = list(
    width = 17.435,
    height = 20,
    path = "m-4.048-.989 3.992 3.667L4.065-.908M-4.064 2.37v2.336h7.982V2.369m-3.992.244v-7.319"
  ),
  click = htmlwidgets::JS("
                        function(e) {
                          Plotly.downloadImage(e.id, {format: 'png', width: 800, height: 600, filename: e.id});
                        }

                            ")
)

plotly::plot_ly(mtcars, x = ~cyl) |>
  plotly::config(
    displaylogo = FALSE,
    modeBarButtonsToAdd = list(dl_button),
    modeBarButtonsToRemove = c(
      "zoomIn2d",
      "zoom2d",
      "pan2d",
      "zoomOut2d",
      "select2d",
      "lasso2d",
      "autoScale2d",
      "resetScale2d",
      "hoverClosestCartesian",
      "hoverCompareCartesian",
      "toImage"
    )
  ) |>
  htmlwidgets::onRender('function(el, x) {
                         $("[data-title=\'Save As Image\'] svg path").attr("fill", "none").attr("stroke-width", "1.176");
                         $("[data-title=\'Save As Image\'] svg").attr("viewBox","-8.717 -10 17.435 20").attr("width", "17.435px").attr("height", "20px");
                        }')

Note that the HTML/svg for the icon in the rendered plot is identical to what's above, yet...

Any ideas as to why?

Start with the R example using plotly::config() with modeBarButtonsToAdd and htmlwidgets::onRender(), then inspect the rendered modeBar SVG in a browser. Reproduce the mismatch between the identical SVG markup and the displayed icon; done when the cause is identified and the custom Download image icon renders as intended.