chrome/browser/resources/compose/result_text.html

<style include="md-select">
  .result-text {
    white-space: pre-wrap;
    word-wrap: break-word;
    user-select: text;
    outline: none;
    cursor: text;
    padding-bottom: 1lh;
    /*One line high, to avoid resizing after first word is added.*/
    min-height: 1lh;
  }

  @keyframes text-fade-in {
    from { opacity: 0;}
    to {opacity: 1;}
  }

  /* Each word fades in when streaming. */
  #partialResultText span {
    animation-name: text-fade-in;
    animation-duration: 200ms;
    animation-timing-function: linear;
  }
</style>
<div id="root">
  <div id="resultText" class="result-text"
      hidden="[[textInput.streamingEnabled]]" contenteditable="plaintext-only"
      on-focusin="onFocusIn_" on-focusout="onFocusOut_"
      aria-label="$i18n{resultText}"></div>
  <div id="partialResultText" class="result-text"
      hidden="[[!textInput.streamingEnabled]]"
      contenteditable$="[[partialTextCanEdit_()]]" on-focusin="onFocusIn_"
      on-focusout="onFocusOut_"
    ><template is="dom-repeat" items="[[displayedChunks_]]"
    ><span>[[item.text]]</span></template></div>
</div>