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<p id="pourcent0">Paragraphe</p>
<p id="pourcent25">Paragraphe</p>
<p id="pourcent50">Paragraphe</p>
<p id="pourcent75">Paragraphe</p>
<p id="pourcent100">Paragraphe</p>
#pourcent0    { background-color: rgba(0, 255, 0, 0); }
#pourcent25   { background-color: rgba(0, 255, 0, 0.25); }
#pourcent50   { background-color: rgba(0, 255, 0, 0.5); }
#pourcent75   { background-color: rgba(0, 255, 0, 0.75); }
#pourcent100  { background-color: rgba(0, 255, 0, 1); }