What is the difference between adding .classA and .classB.classA in CSS?

Tags: , , ,



the problem is when I put .show instead of.box.show in CSS the even boxes don’t come from the left side. I just wanna know why? because I thought they were the same thing. but it seems like in this code they are behaving differently.

const boxes = document.querySelectorAll('.box');

window.addEventListener('scroll',()=>{
    const triggerPoint=window.innerHeight*4/5;
    boxes.forEach((box)=>{
        const boxTop=box.getBoundingClientRect().top;
        if(boxTop<triggerPoint){
            box.classList.add('show')
        }else{
            box.classList.remove('show')
        }
    })
})
*{
    padding:0;
    margin:0;
    box-sizing: border-box;
}


body{
    background-color: #efedd6;
    min-height: 100%;
    width:100%;
    display:flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    overflow-x: hidden;
}

.box{
    width: 100px;
    height: 100px;
    background-color: rgb(226, 43, 43);
    margin:10px;
    transform: translateX(4000%);
    transition:0.4s;
}

h1{
    margin:10px;
}



.box:nth-of-type(even){
    transform: translateX(-4000%);
}
.box.show{
    transform: translateX(0%);
    transition: .4s;
}
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="style.css">
    <title>Scroll Animation</title>
</head>
<body>
    <!-- <h1>scroll to see the Animation</h1> -->
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>


    <script src="main.js"></script>
</body>
</html>

Answer

.classA targets elements with CSS classclassA and has a CSS specificity of 0, 0, 1, 0. Let’s say 10.

classA.classB (or .classB.classA) targets elements with both classes classA and classB. This time with a specificity of 20 (two classes).

Why does this strange word matter in your case?

Your selector with default transform value below has a specificity of 10:

.box{
  transform: translateX(4000%);
}

The following selector

.box:nth-of-type(even){
   transform: translateX(-4000%);
}

has a specificity of 20, and will override same CSS attributes from selectors with lower specificity. So your even animation works by overriding .box{transform: translateX(4000%);}.

But .show{ transform: translateX(0%); } doesn’t have a higher specificity, so it can fail to override the original value.

.box.show{transform: translateX(0%);} however, has specificity of 20 and will definitely override the original value just like the selector for even elements.

Read more about specificity with illustrations here: specifics-on-css-specificity



Source: stackoverflow