JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div class="child-item"></div>
    <div class="child-item"></div>
    <div class="child-item"></div>
    <div class="child-item"></div>
    <div class="child-item"></div>
    <div class="child-item"></div>
    <div class="ghost-item"></div>
    <div class="ghost-item"></div>
    <div class="ghost-item"></div>
    <div class="ghost-item"></div>
    <div class="ghost-item"></div>
    <div class="ghost-item"></div>
    <div class="ghost-item"></div>
</div>

CSS

#container {
    #align-content: flex-start; /* not necessarily needed */
    background-color: red;
    display: flex;
    flex-flow: row wrap;
    #height: 200px; /* no height in a responsive layout */
    #justify-content: space-around; /* the items stretch anyway */
    padding: 10px;
    #width: 400px; /* no width in a responsive layout */
}

.child-item {
    background-color: yellow;
    flex-basis: 75px;
    flex-grow: 1;
    height: 20px;
    margin: 10px;
    #width: 75px; /* flex-basis covers this */
}

.ghost-item {
    #background-color: transparent; /* can't see it anyway */
    flex-basis: 75px;
    flex-grow: 1;
    height: 0px;
    margin: 0 10px; /* removed the top/bottom margin */
    #width: 75px; /* flex-basis covers this */
}