<div id="parent">
  <div class="child">A</div>
  <div class="child">B</div>
  <div class="child">C</div>
  <dov class="child">D</div>
</div>

#parent {
  display: flex;
}

.child {
  background-color: yellow;
  
  flex-basis: 100px;
  flex-grow:1;
  flex-shrink:0;
  
  margin-left: 10px;
}