Angular materialをのダイアログを下記のように書きました。しかし、一番下にある<md-dialog-actionsが1番上に表示されてしまいます。なぜでしょうか。

<md-dialog aria-label="Post Question" ng-clock>
  <form>
    <md-toolbar>
      <div class="md-toolbar-tools">
        <h2>Post Question</h2>
        <span flex></span>
        <md-button class="md-icon-button" ng-click="cancell()">
          <md-icon md-svg-src="img/close.svg" aria-label="Close dialog"></md-icon>
        </md-button>
      </div>
    </md-toolbar>
    <md-dialog-content style="max-width:800px;max-height:810px; ">
      <div class="md-dialog-content">
        <md-input-container>
          <label>Title</label>
          <input ng-model="question.title" md-autofocus>
        </md-input-container>
        <md-list>
          <md-subheader class="md-no-sticky">Selections</md-subheader>
          <md-list-item ng-repeat="selection in question.selections">
            <div class="md-list-item-text" layout="column">
              <md-input-container>
                <label>Selection{{ $index }}</label>
                <input ng-model="selection.content">
              </md-input-container>
            </div>
          </md-list-item>
        <div layout="row">
          <span flex></span>
          <md-button class="md-icon-button" ng-click="addSelection()">
            <md-icon md-svg-src="img/add_box.svg" aria-label="Add Selection"></md-icon>
          </md-button>
        </div>
      </div>
    </md-dialog-content>
    <md-dialog-actions layout="row">
      <span flex></span>
      <md-button ng-click="post(question)" style="margin-right:20px;">Post</md-button>
    </md-dialog-actions>
  </form>
</md-dialog>