Transparent Box

With opacity:

{opacity:0.1}

{opacity:0.3}

{opacity:0.6}

{opacity:1.0}

With RGBA color values:

{background-color: rgba(76, 175, 80, 0.1);}

{background-color: rgba(76, 175, 80, 0.3);}

{background-color: rgba(76, 175, 80, 0.6);}

{background-color: rgba(76, 175, 80);}