chrome/browser/resources/pdf/elements/viewer-annotations-bar.html

<style include="pdf-shared">
  :host {
    align-items: center;
    background-color: rgb(32, 33, 34);
    color: var(--pdf-toolbar-text-color);
    display: flex;
    height: 48px;
    justify-content: center;
    padding: 0 16px;
  }

  #pen,
  #highlighter {
    --dropdown-width: 346px;
  }

  #pen,
  #highlighter {
    --dropdown-open-background: var(--pdf-viewer-background-color);
  }

  #eraser {
    opacity: 0.38;
  }

  #eraser[selected],
  #eraser:focus,
  #eraser:hover {
    opacity: 1;
  }

  #annotation-separator {
    background: white;
    height: 30px;
    margin-inline-end: 12px;
    margin-inline-start: 12px;
    opacity: 0.38;
    width: 1px;
  }

  #pen {
    margin-inline-end: 10px;
  }

  #highlighter {
    margin-inline-end: 6px;
  }
</style>
<viewer-toolbar-dropdown id="pen"
    selected$="[[isAnnotationTool_('pen', annotationTool_.tool)]]"
    open-after-select
    on-click="annotationToolClicked_"
    open-icon="pdf:marker"
    closed-icon="pdf:marker"
    dropdown-centered
    hide-header
    header="$i18n{annotationPen}"
    style="--pen-tip-fill: #000000">
  <viewer-pen-options
    selected-color="#000000"
    selected-size="0.1429"
    strings="[[strings]]"
    on-selected-size-changed="annotationToolOptionChanged_"
    on-selected-color-changed="annotationToolOptionChanged_">
  </viewer-pen-options>
</viewer-toolbar-dropdown>

<viewer-toolbar-dropdown id="highlighter"
    selected$="[[isAnnotationTool_('highlighter', annotationTool_.tool)]]"
    open-after-select
    on-click="annotationToolClicked_"
    open-icon="pdf:highlighter"
    closed-icon="pdf:highlighter"
    dropdown-centered
    hide-header
    header="$i18n{annotationHighlighter}"
    style="--pen-tip-fill: #ffbc00">
  <viewer-pen-options
    selected-color="#ffbc00"
    selected-size="0.7143"
    strings="[[strings]]"
    on-selected-size-changed="annotationToolOptionChanged_"
    on-selected-color-changed="annotationToolOptionChanged_">
  </viewer-pen-options>
</viewer-toolbar-dropdown>

<cr-icon-button id="eraser"
    selected$="[[isAnnotationTool_('eraser', annotationTool_.tool)]]"
    on-click="annotationToolClicked_" iron-icon="pdf:eraser"
    aria-label="$i18n{annotationEraser}"
    title="$i18n{annotationEraser}"></cr-icon-button>

<div id="annotation-separator"></div>

<cr-icon-button id="undo" disabled="[[!canUndoAnnotation_]]"
    iron-icon="pdf:undo" on-click="onUndoClick_"
    aria-label="$i18n{annotationUndo}"
    title="$i18n{annotationUndo}"></cr-icon-button>

<cr-icon-button id="redo" disabled="[[!canRedoAnnotation_]]"
    iron-icon="pdf:redo" on-click="onRedoClick_"
    aria-label="$i18n{annotationRedo}"
    title="$i18n{annotationRedo}"></cr-icon-button>