Border colour option

In Shiny we have `splitLayout()` function that puts multiple plots side by side and takes `style=` argument, e.g.:

``` R
splitLayout(
style = "border: 1px solid silver;",
cellWidths = 300,
cellArgs = list(style = "padding: 6px"),
plotOutput("plot1"),
plotOutput("plot2"),
plotOutput("plot3")
)
```

This is great to put plots side by side and add borders, but I am trying plot one after another vertically, and **have borders**.

Can we have `style=` argument for `forceNetworkOutput()`, e.g.:

``` R
forceNetworkOutput("plotGraphLD_StepwiseForward",
style = "border: 1px solid silver;")
```

Or if there is a JS tag option to achieve this, please share an example.

Thanks