JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
</div>

CSS

.item {
    float: left;
    width: 100px;
    height: 50px;
    background: green;
    margin: 5px;
    transition: opacity 1s;
    -webkit-transition: opacity 1s; 
}

.item:hover {
    opacity: 1 !important;
}
.wrapper:hover .item {
    opacity: 0.5;
    transition: opacity 1s;
     -webkit-transition: opacity 1s;  
}