<div class="frame">
  <b>Color</b></br>

  (Red, Green, Blue)<br/>(
<input type=text size=3 id="red" value="150" onChange="javascript: changeColors();">,
<input type=text size=3 id="green" value="0" onChange="javascript: changeColors();">,
<input type=text size=3 id="blue" value="100" onChange="javascript: changeColors();">)<br/>
  <div id="color1Preview">
    </div>
</div>
<div class="frame">
  <b>Opposite Color</b></br>

  (Red, Green, Blue)<br/>(<input type=text size=3 id="oppositeRed" value="105" disabled>,<input type=text size=3 id="oppositeGreen" value="255" disabled>,<input type=text size=3 id="oppositeBlue" value="155" disabled>)<br/>
  <div id="color2Preview">
    </div>
</div> 

BODY {
  background-color: #333333;
}

.frame {
  float: left;
  margin: 10px;
  background-color: #DDDDDD;
  border: 1px solid #666666;
  border-radius: 10px;
  width: 200px;
  padding: 10px;
  text-align: center;
  line-height: 1.5;
  font-family: courier new;
  font-size: 10pt;
 -webkit-box-shadow: 3px 3px 3px 0px rgba(0,0,0,0.25);
-moz-box-shadow: 3px 3px 3px 0px rgba(0,0,0,0.25);
box-shadow: 3px 3px 3px 0px rgba(0,0,0,0.25);   
}

INPUT {
  text-align: right;
}

#color1Preview {
  background-color: rgb(150,0,100);
}
#color2Preview {
  background-color: rgb(105,255,155);
}

#color1Preview, #color2Preview {
  width: 100px;
  height: 100px;
  border-radius: 50%;
  margin: 10px auto;
-webkit-box-shadow: 3px 3px 3px 0px rgba(0,0,0,0.55);
-moz-box-shadow: 3px 3px 3px 0px rgba(0,0,0,0.55);
box-shadow: 3px 3px 3px 0px rgba(0,0,0,0.55);  
}

function changeColors() {
  var r,g,b;

  //Retrieve user input
  r=document.getElementById("red").value;
  g=document.getElementById("green").value;
  b=document.getElementById("blue").value;
  console.log(r,g,b)  //Preview Color
  document.getElementById("color1Preview").style.backgroundColor = `rgb(${r},${g},${b})`;
  
  alert("Complete the code to calculate and preview the opposite color code.");
  
  document.getElementById("color2Preview").style.backgroundColor = `rgb(${255-r},${255-g},${255-b})`;
}