A card container with optional header and body. Supports always, hover,
and never shadow modes.
Examples
el_card(shiny::tags$p("Card body text."), header = "My Card")
#> <div class="el-card is-always-shadow">
#> <div class="el-card__header">My Card</div>
#> <div class="el-card__body">
#> <p>Card body text.</p>
#> </div>
#> </div>
el_card(shiny::tags$p("No shadow."), shadow = "never")
#> <div class="el-card is-never-shadow">
#> <div class="el-card__body">
#> <p>No shadow.</p>
#> </div>
#> </div>