JSFiddle - React, Tailwind, and code Playground

HTML

<!--
  Centers a group of boxes that wrap to the width of its container.
  Also left-aligns them inside the container.
  Issue: Does not center group if there aren't enough boxes to fill
  the first row.
  -->
<div class="container">
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    <div class="block"></div>
    
    <!--
      How many placeholders do you need?
      At least the number of blocks minus two.
      -->
    <div class="placeholder"></div>
    <div class="placeholder"></div>
    <div class="placeholder"></div>
    <div class="placeholder"></div>
    <div class="placeholder"></div>
    <div class="placeholder"></div>
    <div class="placeholder"></div>
    <div class="placeholder"></div>
</div>

CSS

body {
    text-align: center;     /* center a max-width container */
    font-size: 0;           /* remove spaces between blocks */
}
.container {                /* you don't need this */
    background-color: #eee; /* so you can see what's happening */
    max-width: 960px;       /* to demonstrate the centering of a max-width container */
    display: inline-block;  /* center the max-width container */
    text-align: center;     /* center the group of blocks */
}
.block {
    display: inline-block;  /* left-align within the group */
    background-color: red;  /* so you can see what's happening */
    height: 100px;
    width: 100px;
    margin: 10px;
}
.placeholder {
    display: inline-block;  /* add to the line of blocks */
    width: 120px;           /* width + margin of a block */
}