flex items are not centering

Question

I have the following layout which populates a containing div with a number of circles representing team members. I have an odd caveat at the moment where the intended outcome is achieved for teams consisting of >= 3 team members, however for teams which only consist of 1 || 2 members, the circles align to the far left of the container.

Why is this the case?

.fireteam {
  padding: 0 5px;
}

.fireteam>p {
  max-width: 100%;
  overflow: hidden;
  white-space: nowrap;
  margin: 0 0 0.1rem;
}

.fireteam #fireteamMembers {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  align-content: center;
  justify-content: center;
  height: 4.2rem;
  list-style: none;
  padding: 0;
  border: 1px solid #000;
  border-radius: 5px;
  overflow: hidden;
}

.fireteam .fireteamMember {
  width: 1.5rem;
  height: 1.5rem;
  background: #000;
  color: white;
  border-radius: 50%;
  margin: 0.25rem;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>

Answer 1

Your flex containers are missing align-items: center.

Add this to your code:

.fireteam #fireteamMembers {
  align-items: center; /* NEW */
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  align-content: center;
  justify-content: center;
  height: 4.2rem;
  list-style: none;
  padding: 0;
  border: 1px solid #000;
  border-radius: 5px;
  overflow: hidden;
}

.fireteam {
  padding: 0 5px;
}

.fireteam>p {
  max-width: 100%;
  overflow: hidden;
  white-space: nowrap;
  margin: 0 0 0.1rem;
}

.fireteam #fireteamMembers {
  align-items: center; /* NEW */
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  align-content: center;
  justify-content: center;
  height: 4.2rem;
  list-style: none;
  padding: 0;
  border: 1px solid #000;
  border-radius: 5px;
  overflow: hidden;
}

.fireteam .fireteamMember {
  width: 1.5rem;
  height: 1.5rem;
  background: #000;
  color: white;
  border-radius: 50%;
  margin: 0.25rem;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>
<div class="fireteam col-xs-4">
  <p>name</p>
  <label>X members</label>
  <ul id="fireteamMembers">
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
    <li class="fireteamMember"></li>
  </ul>
</div>

In your column-direction container, only two circles can fit in a column. The next one wraps.

Once there is a wrap, the container has multiple flex lines, and align-content is needed to center them. You have this already. That's why >=3 works.

But when there are only one or two circles, there is only one flex line and align-content has no effect. That's why 1 & 2 circles aren't centering. You need align-items to center the items in a single line flex container.

Here's a more complete explanation:

• How does flex-wrap work with align-self, align-items and align-content?