Flexbox - 容器宽度自动

Question

如何使ul中.menu-sub-col的宽度等于内容宽度？

https://fiddle.jshell.net/j9ujfL2n/3/

.menu {
  position: absolute;
  z-index: 90;
  display: flex;
  flex-direction: row;
  top: 40px;
  left: 0;
  transition: transform 0.25s ease-in-out;
  transform: translateY(-100%);
  visibility: hidden;
}
.menu--visible {
  transform: translateY(0);
  visibility: visible;
}
.menu ul {
  list-style-type: none;
  padding: 0;
  margin: 0;
}
.menu li {
  cursor: pointer;
}

.menu-main {
  background-color: #3E5AE2;
  box-shadow: 0px 4px 10px rgba(0, 0, 0, 0.2);
  height: max-content;
}
.menu-main li {
  position: relative;
  padding: 10px 20px;
  border-bottom: 1px solid rgba(0, 0, 0, 0.2);
  color: rgba(255, 255, 255, 0.7);
  font-size: 14px;
}
.menu-main li:hover {
  color: #fff;
}
.menu-main li.active {
  background-color: #4B67E8;
  color: #fff;
}
.menu-main li.active:after {
  content: '';
  position: absolute;
  right: -8px;
  top: calc(50% - 8px);
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 8px 0 8px 8px;
  border-color: transparent transparent transparent #4B67E8;
  clear: both;
}
.menu-main li i {
  margin-right: 15px;
}

.menu-sub:not(:empty) {
  padding: 20px 30px;
  display: flex;
  flex-direction: row;
  background: #fff;
  box-shadow: 0px 4px 10px rgba(0, 0, 0, 0.2);
}

.menu-sub-col {
  padding-right: 25px;
}
.menu-sub-col:not(:last-child) {
  border-right: 1px solid #eeeeee;
  margin-right: 25px;
}
.menu-sub-col h4 {
  color: #bdbdbd;
  font-size: 12px;
  text-transform: uppercase;
}
.menu-sub-col ul {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  align-content: space-between;
  max-height: 180px;
}
.menu-sub-col li {
  flex: 1 1 auto;
  font-size: 12px;
  font-weight: 500;
  padding: 5px 4px;
  padding-left: 0;
  opacity: 0.75;
}
.menu-sub-col li:hover {
  color: #ffffff;
  opacity: 1;
  background: #4b67e9;
  box-shadow: -10px 0px 0px #4b66ea, 10px 0px 0px #4b66ea;
  transition: box-shadow 0.2s ease, background 0.2s ease, box-shadow 0.2s ease, color 0.2s ease;
  border-radius: 3px;
}
.menu-sub-col li i {
  margin-right: 8px;
}

<div class="menu menu--visible">
  <div class="menu-main">
    <ul>
      <li class=""><i class="mdi mdi-earth"></i>Monitoring</li>
      <li class="active"><i class="mdi mdi-file-chart"></i>Raporty</li>
      <li class=""><i class="mdi mdi-format-list-bulleted"></i>Ewidencja</li>
      <li class=""><i class="mdi mdi-settings"></i>System</li>
    </ul>
  </div>
  <!---->
  <div data-subname="reports" class="menu-sub">
    <div class="menu-sub-col">
      <h4>Pojazdy</h4>
      <ul>
        <li><i class="mdi mdi-earth"></i>Trasa</li>
        <li><i class="mdi mdi-earth"></i>Doby</li>
        <li><i class="mdi mdi-earth"></i>Bazy</li>
        <li><i class="mdi mdi-earth"></i>Id</li>
        <li><i class="mdi mdi-earth"></i>Paliwo</li>
        <li><i class="mdi mdi-earth"></i>Prędkości</li>
        <li><i class="mdi mdi-earth"></i>Praca silnika</li>
        <li><i class="mdi mdi-earth"></i>Liczniki</li>
        <li><i class="mdi mdi-earth"></i>Pryw. Firm</li>
        <li><i class="mdi mdi-earth"></i>Statusy pracy</li>
        <li><i class="mdi mdi-earth"></i>Kursy</li>
        <li><i class="mdi mdi-earth"></i>Przeglądy</li>
        <li><i class="mdi mdi-earth"></i>PIAP</li>
        <li><i class="mdi mdi-earth"></i>PLK</li>
      </ul>
    </div>
    <div class="menu-sub-col">
      <h4>Kierowcy</h4>
      <ul>
        <li><i class="mdi mdi-earth"></i>Obsada</li>
        <li><i class="mdi mdi-earth"></i>Id</li>
      </ul>
    </div>
    <div class="menu-sub-col">
      <h4>Punkty własne</h4>
      <ul>
        <li><i class="mdi mdi-earth"></i>Dla pojazdu</li>
        <li><i class="mdi mdi-earth"></i>Dla POI</li>
      </ul>
    </div>
  </div>
  <!---->
  <!---->
</div>