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class=" yui3-js-enabled
      js
      flexbox
      canvas
      canvastext
      webgl
      no-touch
      hashchange
      history
      draganddrop
      rgba
      hsla
      multiplebgs
      backgroundsize
      borderimage
      borderradius
      boxshadow
      textshadow
      opacity
      cssanimations
      csscolumns
      cssgradients
      cssreflections
      csstransforms
      no-csstransforms3d
      csstransitions
      video
      audio
      svg
      inlinesvg
      svgclippaths
      wf-futurapt-n4-active
      wf-futurapt-n5-active
      wf-bebaskai-n4-active
      wf-futurapt-n7-active
      wf-hypatiasanspro-n2-active
      wf-hypatiasanspro-n4-active
      wf-hypatiasanspro-n6-active
      wf-hypatiasanspro-n7-active
      wf-futurapt-i4-active
      wf-futurapt-n3-active
      wf-futurapt-i5-active
      wf-futurapt-i7-active wf-active"

#p1 {background-color:rgba(255,0,0,0.3);} /* red with opacity*/

<html class="rgba">