library(shiny)
library(bsplus)
lorem_ipsum <- "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."
ui <- fluidPage(
  tags$style(HTML('
    /* Icon when the collapsible content is shown */
    .collbtn:after {
    content: "-";
    float: right;
    margin-left: 10px;
    }
    /* Icon when the collapsible content is hidden */
    .collbtn.collapsed:after {
    content: "+";
    }
    ')),
  titlePanel("bs_attach_collapse with custom classes"),
  fluidPage(
    column(
      width = 4,
      bs_button("show = TRUE, class lost", class = "collbtn") %>%
        bs_attach_collapse("panel-A"),
      bs_collapse("panel-A", show = TRUE, wellPanel(lorem_ipsum))
    ),
    column(
      width = 4,
      bs_button("show = TRUE, class added", class = "collbtn") %>%
        bs_attach_collapse("panel-B") %>%
        tagAppendAttributes(class = "collbtn"),
      bs_collapse("panel-B", show = TRUE, wellPanel(lorem_ipsum))
    ),
    column(
      width = 4,
      bs_button("show = FALSE, class added", class = "collbtn collapsed") %>%
        bs_attach_collapse("panel-C") %>%
        tagAppendAttributes(class = "collbtn collapsed"),
      bs_collapse("panel-C", show = FALSE, wellPanel(lorem_ipsum))
    )

  )
)
server <- function(input, output) {}
shinyApp(ui = ui, server = server)