.footer {
  width: 300px;
  height: 20px;
  display: flex;
  overflow: hidden;
}
.left {
  background: #3cc8b4;
  flex: 1 1 auto;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  min-width: 50px;
}
.right {
  background: #9bc;
  max-width: 250px;
}
.right-ellipsis {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

<div class="footer">
   <div class="left">
     leftleftleftleftleftleftleftleftleftleftleftleftleft
  </div>
  <div class="right">
    <div class="right-ellipsis">
      rightrightrightrightrightrightrightrightright
    </div>
  </div>
</div>