JSFiddle - React, Tailwind, and code Playground

HTML

<div class="openinghours floatRight">
    <div class="content">This is some dummy text. It's supposed to be black - not transparent.</div>
</div>

CSS

.openinghours { 
  height: 70px;
  width: 300px;
  padding: 10px;
  font-size: 0.85em;
  background-color: #f6f6f6; 
  border: solid 1px #c7c7c7;
  margin-right: 20px;
  margin-top: 5px;
  opacity: .5;
  filter: alpha(opacity=50);
  border-radius: 5px;
  -moz-border-radius: 5px;
  -webkit-border-radius: 5px; 
}

.openinghours .content {
  color: #000;
}