Tailwind CSS class .border-opacity-25 / border-*-#

<div class="border-opacity-0 border-4 border-teal-600 p-4"></div>
<div class="border-opacity-25 border-4 border-teal-600 p-4"></div>
<div class="border-opacity-50 border-4 border-teal-600 p-4"></div>
<div class="border-opacity-100 border-4 border-teal-600 p-4"></div>

.border-opacity-0 { --border-opacity: 0; }
border-opacity-25 { --border-opacity: 0.25; }
border-opacity-50 { --border-opacity: 0.5; }
border-opacity-75 { --border-opacity: 0.75; }
border-opacity-100 { --border-opacity: 1; }