Polymer Paper选项卡可滚动问题

Question

在Polymer 1.0中，当我尝试为选项卡添加可滚动选项时，宽度似乎变为0.

<paper-toolbar id="mainToolbar">
    <paper-icon-button id="paperToggle" icon="menu" paper-drawer-toggle></paper-icon-button>
    <span class="flex"></span>

    <!-- Toolbar icons -->
    <paper-icon-button icon="refresh"></paper-icon-button>
    <paper-icon-button icon="search"></paper-icon-button>

    <!-- Application name -->
    <div class="middle paper-font-display2 app-name">Polymer Starter Kit</div>

    <!-- Tabs -->
    <paper-tabs id="scrollableTabs" tabindex="0" selected="0" scrollable class="bottom x-scope self-end paper-tabs-0">
        <paper-tab>Bordeaux</paper-tab>
        <paper-tab>Burgundy</paper-tab>
        <paper-tab>Champagne</paper-tab>
        <paper-tab>Rhone</paper-tab>
        <paper-tab>France</paper-tab>
        <paper-tab>Italy</paper-tab>
        <paper-tab>Spain</paper-tab>
        <paper-tab>Americas</paper-tab>
        <paper-tab>Australia & NZ</paper-tab>
        <paper-tab>Rest of World</paper-tab>
        <paper-tab>Spirits & Fortifieds</paper-tab>
    </paper-tabs>

</paper-toolbar>

如果我删除了可滚动条，它们会正常显示。

文档说If true, tabs are scrollable and the tab width is based on the label width.那很好......但是在哪里设置标签宽度？