chrome/browser/resources/extensions/code_section.html

<style include="cr-hidden-style">
  :host {
    --container-bg: white;
    --line-bg: var(--paper-grey-300);
    --main-color: var(--paper-grey-800);
    display: block;
  }

  @media (prefers-color-scheme: dark) {
    :host {
      --container-bg: rgba(0, 0, 0, .4);
      --line-bg: var(--google-grey-800);
      --main-color: var(--cr-primary-text-color);
    }
  }

  #scroll-container {
    background: var(--container-bg);
    height: 100%;
    overflow: auto;
    position: relative;
  }

  @media (prefers-color-scheme: light) {
    #scroll-container {
      border: 1px solid var(--paper-grey-500);
    }
  }

  #main {
    color: var(--main-color);
    display: flex;
    font-family: monospace;
    min-height: 100%;
  }

  #line-numbers {
    background: var(--line-bg);
    display: flex;
    flex-direction: column;
    padding: 0 8px;
    text-align: end;
  }

  @media (prefers-color-scheme: light) {
    #line-numbers {
      border-inline-end: 1px solid var(--paper-grey-500);
    }
  }

  #source {
    display: flex;
    flex-direction: column;
    margin-inline-start: 4px;
  }

  #line-numbers span,
  #source span {
    white-space: pre;
  }

  #no-code {
    text-align: center;
  }

  @media (prefers-color-scheme: light) {
    #no-code {
      color: var(--paper-grey-800);
    }

    .more-code {
      color: var(--paper-grey-500);
    }
  }

  #highlight-description {
    height: 0;
    overflow: hidden;
  }

  @media (prefers-color-scheme: dark) {
    mark {
      background-color: var(--google-yellow-refresh-300);
      color: var(--google-grey-900);
    }
  }
</style>
<div id="scroll-container" hidden="[[!highlighted_]]" dir="ltr">
  <div id="main">
    <!-- Line numbers are not useful to a screenreader -->
    <div id="line-numbers" aria-hidden="true">
      <div class="more-code before" hidden="[[!truncatedBefore_]]">
        ...
      </div>
      <span>[[lineNumbers_]]</span>
      <div class="more-code after" hidden="[[!truncatedAfter_]]">
        ...
      </div>
    </div>
    <div id="source">
      <div class="more-code before" hidden="[[!truncatedBefore_]]">
        [[getLinesNotShownLabel_(
            truncatedBefore_,
            '$i18nPolymer{errorLinesNotShownSingular}',
            '$i18nPolymer{errorLinesNotShownPlural}')]]
      </div>
      <span><!-- Whitespace is preserved in this span. Ignore new lines.
        --><span>[[before_]]</span><!--
        --><mark aria-label$="[[highlighted_]]"
            aria-describedby="highlight-description"><!--
          --><span aria-hidden="true">[[highlighted_]]</span><!--
        --></mark><!--
        --><span>[[after_]]</span><!--
      --></span>
      <div class="more-code after" hidden="[[!truncatedAfter_]]">
        [[getLinesNotShownLabel_(
            truncatedAfter_,
            '$i18nPolymer{errorLinesNotShownSingular}',
            '$i18nPolymer{errorLinesNotShownPlural}')]]
      </div>
    </div>
  </div>
</div>
<div id="no-code" hidden="[[!showNoCode_]]">[[couldNotDisplayCode]]</div>
<div id="highlight-description" aria-hidden="true">
  [[highlightDescription_]]
</div>