Using the bootstrap grid

<div class="modal-body">
  <div class="container-fluid">
    <div class="row">
      <div class="col-md-4">.col-md-4</div>
      <div class="col-md-4 ml-auto">.col-md-4 .ml-auto</div>
    </div>
    <div class="row">
      <div class="col-md-3 ml-auto">.col-md-3 .ml-auto</div>
      <div class="col-md-2 ml-auto">.col-md-2 .ml-auto</div>
    </div>
    <div class="row">
      <div class="col-md-6 ml-auto">.col-md-6 .ml-auto</div>
    </div>
    <div class="row">
      <div class="col-sm-9">
        Level 1: .col-sm-9
        <div class="row">
          <div class="col-8 col-sm-6">
            Level 2: .col-8 .col-sm-6
          </div>
          <div class="col-4 col-sm-6">
            Level 2: .col-4 .col-sm-6
          </div>
        </div>
      </div>
    </div>
  </div>
</div>