<div class="about__list-left">
  <div class="round-element"></div>
</div>

.about__list-left {
  display: flex;
  justify-content: flex-start;  /* либо значение flex-end  */
  width: 100%;
  border: 1px dotted red;
  height: 200px;
}

.round-element {
  background: green;
  width: 100px;
  height: 100px;
  border-radius: 50%;
  margin: auto;
}