@f.ehler.i.nolim plus points for trying and sharing your code. As I am a nice person I cooked up this for you
New-UDColumn -Size 3 -Content {
New-UDStyle -Style '.fa-sm {
font-size: 6em;
opacity: 0.2;
float: left;
position: absolute;
top: 20px;
margin-left: 145px;
}' -Content {
New-UDCard -Id "Families22" -title "No. of Families" -Content {
New-UDIcon -Icon 'group'
New-UDHeading -Size 5 -Text "Look at this"
}
}
}
Which gives me:-

Which now gives the appearance of a watermark effect of the icon…I right clicked the icon inspect element, found the font-size stored under .fa-sm
so started added more css elements to this which @AlonGvili had kindly shared and I re-quoted for you, then binded this to UniversalDashboard.Style module, which allowed me to style this particular icon for this particular card. I hope this answers your question
P.S I am releasing the speech bubble as a custom component
One last thing, I just finished this blog on another component I built, which again uses UniversalDashboard.Style to spruce it up a bit, do have a read:-