message: Add styles for arena embeds on blog
diff: max-width 80%
  margin 2em auto
  display block
  + height 800px !important
  img
  max-width 100%
  .arena-iframe
  - border 1px solid colors-gray-border
  - box-shadow 4px 4px 4px colors-gray-background
  - height 2150px !important
  + height 560px !important
  + max-width 100%
  margin 4em auto
  padding 1px
  display block
  +mobile()
  margin 4em 0
  min-width 95%
  - +below(400px)
  - height 500px !important
  + height 770px !important
  h1, h2, h3, h4, h5, h6
  collapsed-margins(.5em)
  left 50%
  transform translate(-50%, -50%)
  +
  +
  &__overlay
  position absolute
  top 0
  