flexbox-wrapped-items

HTML

<ul class="flexcontainer">
    <li>Item One</li>
    <li>Item Two</li>
    <li>Item Three</li>
    <li>Item Four</li>
    <li>Item Five</li>
    <li>Item Six</li>
    <li>Item Seven</li>
    <li>Item Eight</li>
    <li>Item Nine</li>
</ul>

CSS

.flexcontainer {
  display:flex;
  flex-wrap: wrap;
}
.flexcontainer li {
  border-right: 3px solid #c00;
  list-style: none;
  flex: 0 0 100px;
  padding: 10px;
}
.flexcontainer li:last-item-in-row {
  border-right: none;
}