Can CSS be used for creating unique color combinations?

I am facing a challenge where I have two div elements with different transparent, colored backgrounds that overlap each other.

My goal is to find a way to customize the color in the area where these elements overlap.

For instance, if I blend red and blue with an opacity of 0.5, I would like the overlapping region to appear black. Is this achievable? Such a solution would greatly simplify the implementation process.

To provide a clearer illustration, consider the following example:

.wrapper{
  width: 200px;
  height: 500px;
  background-color: #fff;
  position: relative;
}
.box{
  width: 100%;
  position: absolute;
}
.box-1{
  top: 0px;
  height: 250px;
  background-color: rgba(181, 226, 163, 0.5);  
}
.box-2{
  background-color: rgba(183, 222, 241, 0.5);
  top: 200px;
  height: 300px;
}
<div class="wrapper">
  <div class="box box-1">
  </div>
  <div class="box box-2">
  </div>
</div>

UPDATE:

The specific height of the overlapped area is unknown, so simply adding a rigid element with a fixed height such as 50px is not a viable approach. The core question revolves around finding a method to custom mix colors in this scenario.

Answer №1

To achieve this visual effect, the CSS property mix-blend-mode is utilized with a value of multiply. It should be noted that this approach is not compatible with Internet Explorer.

<!DOCTYPE html>
<html>

  <head>
    <style>
      div{
        width:100px;
        height:100px;
        opacity:1;
      }
      .red{
        background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFBQIAX8jx0gAAAABJRU5ErkJggg==);
      }
      .blue{
        background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNkYPj/HwADBwIAMCbHYQAAAABJRU5ErkJggg==);
        mix-blend-mode: multiply
      }
    </style>
  </head>

  <body>
    
    <div class="red">
    </div>
    <div style="position:absolute;top:90px" class="blue">
    </div>
  </body>

</html>

Answer №2

To create a similar effect, you can apply an absolutely positioned pseudo-element ::after to the element with the class .box-1. This pseudo-element should be positioned at the bottom (bottom: 0;) and have a height calculated as 100% of its parent container (.box-1), minus the vertical offset value of .box-2.

For example, if the top value of .box-2 is set to 200px, then the height of the ::after pseudo-element on .box-1 would be:

height: calc(100% - 200px); /* 200px is the top value of .box-2 */

Here is a demo showcasing this technique applied to .box-1 with different heights and the last .box-1 being resizable:

.wrapper{
  display: inline-block;
  width: 200px;
  height: 500px;
  background-color: #fff;
  position: relative;
}

.box{
  width: 100%;
  position: absolute;
}

.box-1{
  top: 0px;
  background-color: rgb(128,191,128);
}

.box-2{
  top: 200px;
  height: 300px;
  background-color: rgb(128,128,255);
}

.wrapper .box-1 {
z-index: 6;
}

.wrapper .box-1::after {
content: '';
position: absolute;
left: 0;
bottom: 0px;
width: 100%;
height: calc(100% - 200px); /* 200px is the top value of .box-2 */
background-color: rgba(0,0,0,1);
}

div:nth-of-type(1).wrapper .box-1 {
height: 250px;
}

div:nth-of-type(2).wrapper .box-1 {
height: 275px;
}

div:nth-of-type(3).wrapper .box-1 {
height: 300px;
}

div:nth-of-type(4).wrapper .box-1 {
height: 325px;
}


div:nth-of-type(4).wrapper .box-1 {
resize: vertical;
overflow: auto;
}
<div class="wrapper">
  <div class="box box-1">
  </div>
  <div class="box box-2">
  </div>
</div>

<div class="wrapper">
  <div class="box box-1">
  </div>
  <div class="box box-2">
  </div>
</div>

<div class="wrapper">
  <div class="box box-1">
  </div>
  <div class="box box-2">
  </div>
</div>

<div class="wrapper">
  <div class="box box-1">
  </div>
  <div class="box box-2">
  </div>
</div>

Answer №3

It may seem like a lot of work, but this method is necessary to achieve the desired outcome.

By using javascript, you can detect overlaps and create div elements to represent the overlapped areas, coloring them black. Below is a simple example code snippet:

UPDATE:

After reading a comment stating the need for functionality across multiple elements, not just two, I have updated the snippet to accommodate multiple elements with the class type overlappable-box. This allows for overlap calculations on any element with that class.

The function clearOverlaps is included in the snippet to clear any calculated overlaps, which is essential for dynamic pages.

function clearOverlaps() {
  overlaps = document.getElementsByClassName("box-overlap");
  var i = 0;
  for (i = 0; i < overlaps.length; i++) {
    document.body.removeChild(overlaps[i]);
  }
}

function addOverlap(box1, box2) {
  // Function code here
}

var overlappableBoxes = document.getElementsByClassName("overlappable-box");
var i = 0;
var j = 0;
var box1;
var box2;
for (i = 0; i < overlappableBoxes.length; i++) {
  box1 = overlappableBoxes[i];
  for (j = i + 1; j < overlappableBoxes.length; j++) {
    box2 = overlappableBoxes[j];
    addOverlap(box1, box2);
  }
}
.styling classes here...
<div></div>

Answer №4

Absolutely. However, achieving this requires the addition of another element that covers the overlapping section. To illustrate this concept, I will modify the dimensions of the div elements to clearly display the borders.

Take a look at this:

div {position:absolute; border:1px solid black;}
#div1 { background:red; opacity:.5; top:0; height:110px; width:100px;}
#div2 { background:blue; opacity:.5; top:50px; height:100px;width:175px;}
#div3 { background:black; top:50px; height:50px; z-index:99; width:150px;}
<div id="div1">test</div>
<div id="div2">test</div>
<div id="div3">test</div>

Regarding your second concern: "I am unsure about the height of the overlapped region". This issue can be resolved using JavaScript:

var d1 = document.getElementById("div1");
var d2 = document.getElementById("div2");
var d3 = document.getElementById("div3");  // The element responsible for masking the overlap

// Retrieve the height and top position of the first element
var d1Height = parseInt(window.getComputedStyle(d1).height.replace("px", ""));
var d1Top = parseInt(window.getComputedStyle(d1).top.replace("px", ""));
console.log("div1 height: " + d1Height, ", div1 top: " +  d1Top);

// Obtain the height and top position of the second element
var d2Height = parseInt(window.getComputedStyle(d2).height.replace("px", ""));
var d2Top = parseInt(window.getComputedStyle(d2).top.replace("px", ""));
console.log("div2 height: " + d2Height, "div2 top: " + d2Top);

// Identify the starting point of the overlap
var overlapTop = d1Height - d2Top;
console.log("Overlap begins at: " + overlapTop);

// Determine the height of the overlap
var overlapHeight = (d1Top + d1Height) - overlapTop;
console.log("overlap height: " + overlapHeight);

// Adjust the positioning of the overlapping div via dynamic CSS styling:
d3.style.top = overlapTop + "px";
d3.style.height = overlapHeight + "px";
div {position:absolute; border:1px solid black;}
    #div1 { background:red; opacity:.5; top:0; height:100px; width:100px;}
    #div2 { background:blue; opacity:.5; height:100px; top: 50px; width:175px;}

    /* This is the div that will mask the overlapping area
       Note that a position and height are not set
       The only reason the width is set is to show what area
       it winds up overlapping, but that would be removed from
       this rule and determined in JavaScript, just as the height is */
    #div3 { background:black; z-index:99; width:150px;}
<div id="div1">test</div>
<div id="div2">test</div>
<div id="div3">test</div>

Answer №5

To create a mixed color effect between two boxes, you should adjust the opacity of the boxes themselves rather than altering the opacity of the color. Changing the rgba opacity will only lighten or darken the color on the div. Since divs have a default opacity of 1, if two boxes overlap, only the top box will be visible while the bottom one remains hidden. To achieve your desired result, add opacity:0.5 to both the .box-1 and .box-2 classes, directly affecting the appearance of the div elements.

Answer №6

Do you think something like this might work?

Although, it may not be very beneficial if the height is constantly changing.

.wrapper {
  width: 200px;
  height: 500px;
  background-color: #fff;
  position: relative;
}
.box {
  width: 100%;
  position: absolute;
}
.box-1 {
  top: 0px;
  height: 250px;
  background-color: rgba(181, 226, 163, 0.5);
}
.box-2 {
  background-color: rgba(183, 222, 241, 0.5);
  top: 200px;
  height: 300px;
}
.box-2:before {
  background-color: black;
  height: 50px;
  display: block;
  content: ' ';
}
<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>

<body>
  <div class="wrapper">
    <div class="box box-1">
    </div>
    <div class="box box-2">
    </div>
  </div>
</body>

</html>

Answer №7

You have the option of utilizing CSS gradients:

.box-2 {
    background-color: blue;
    top: 200px;
    height: 300px;
    background: rgb(0,0,0);
    background: -moz-linear-gradient(top, rgba(0,0,0,1) 0%, rgba(0,0,0,1) 12%, rgba(0,0,0,1) 25%, rgba(0,0,0,1) 39%, rgba(44,44,44,1) 50%, rgba(0,0,0,1) 51%, rgba(25,33,255,1) 51%, rgba(25,33,255,1) 65%, rgba(25,33,255,1) 78%, rgba(25,33,255,1) 78%, rgba(25,33,255,1) 100%);
    background: -webkit-linear-gradient(top, rgba(0,0,0,1) 0%,rgba(0,0,0,1) 12%,rgba(0,0,0,1) 25%,rgba(0,0,0,1) 39%,rgba(44,44,44,1) 50%,rgba(0,0,0,1) 51%,rgba(25,33,255,1) 51%,rgba(25,33,255,1) 65%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 100%);
    background: linear-gradient(to bottom, rgba(0,0,0,1) 0%,rgba(0,0,0,1) 12%,rgba(0,0,0,1) 25%,rgba(0,0,0,1) 39%,rgba(44,44,44,1) 50%,rgba(0,0,0,1) 51%,rgba(25,33,255,1) 51%,rgba(25,33,255,1) 65%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 100%);
    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#000000', endColorstr='#1921ff',GradientType=0 );
    opacity: 0.5;
    background: rgb(0,0,0);
    background: -moz-linear-gradient(top, rgba(0,0,0,1) 0%, rgba(0,0,0,1) 12%, rgba(0,25,255,1) 25%, rgba(0,25,255,1) 39%, rgba(0,25,255,1) 49%, rgba(0,25,255,1) 50%, rgba(0,25,255,1) 53%, rgba(0,25,255,1) 53%, rgba(25,33,255,1) 54%, rgba(0,25,255,1) 60%, rgba(25,33,255,1) 65%, rgba(25,33,255,1) 78%, rgba(25,33,255,1) 78%, rgba(25,33,255,1) 100%);
    background: -webkit-linear-gradient(top, rgba(0,0,0,1) 0%,rgba(0,0,0,1) 12%,rgba(0,25,255,1) 25%,rgba(0,25,255,1) 39%,rgba(0,25,255,1) 49%,rgba(0,25,255,1) 50%,rgba(0,25,255,1) 53%,rgba(0,25,255,1) 53%,rgba(25,33,255,1) 54%,rgba(0,25,255,1) 60%,rgba(25,33,255,1) 65%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 100%);
    background: linear-gradient(to bottom, rgba(0,0,0,1) 0%,rgba(0,0,0,1) 12%,rgba(0,25,255,1) 25%,rgba(0,25,255,1) 39%,rgba(0,25,255,1) 49%,rgba(0,25,255,1) 50%,rgba(0,25,255,1) 53%,rgba(0,25,255,1) 53%,rgba(25,33,255,1) 54%,rgba(0,25,255,1) 60%,rgba(25,33,255,1) 65%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 78%,rgba(25,33,255,1) 100%);
    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#000000', endColorstr='#1921ff',GradientType=0 );
    opacity: .8; 
}

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