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Tailwind CSS class: .bg-opacity-10

    <div class="flex items-center">
        <div class="inline-block mr-4 p-4 h-20 w-40 bg-blue-600 bg-opacity-10">bg-opacity-10</div>
        <div class="inline-block p-4 h-20 w-40 bg-blue-600"></div>
    </div>

Preview

bg-opacity-10

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