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    Sombra externa
    box-shadow: 0px 0px 20px #000000;

     

    Sombra externa, interna en RGB con opacidad
    box-shadow: inset 0px -3px 3px rgba(0,0,0,0.6), inset 0px 3px 3px rgba(252,255,255,0.7), 0px 7px 12px -2px rgba(0,0,0,0.8);

     

    Sombra externa, interna en RGB con opacidad
    box-shadow: inset 0px -3px 3px rgba(0,0,0,0.6), inset 0px 3px 3px rgba(252,255,255,0.7), 0px 27px 12px -2px rgba(0,0,0,0.8);