message: Refine single blog post styling
diff: font-weight bold
  > .post-content
  - //
  + margin-bottom 8em
  p
  - collapsed-margins(1em)
  + collapsed-margins(2em)
  font-size font-size-base
  line-height line-height-tall
  img
  iframe
  display block
  - max-width 100%
  + max-width 500px
  vertical-align bottom
  - border 1px solid colors-gray-border
  margin 2em auto
  + img
  + margin 4em auto
  + max-width 100%
  +
  .arena-iframe
  + border 1px solid colors-gray-border
  box-shadow 4px 4px 4px colors-gray-background
  height 2150px !important
  + margin 4em
  padding 1px
  + +mobile()
  + margin 4em 0
  + min-width 100%
  +below(400px)
  height 2000px !important
  +below(380px)
  