How to change css style based on value

If I understand your question correctly, you could add a data-attribute to the HTML element and alter the value (for example with Javascript) to/from "true/false" and use that in your CSS like so:

<element data-status="true">Content</element>
<element data-status="false">Content</element>

[data-status="true"] {
    color: green;
}
[data-status="false"] {
    color: red;
}

$('.test').each(function() {
  if(parseInt($(this).css('font-size')) > 16) {
    $(this).css('color', 'green');
  }
});

.test {
  font-size: 18px;
  color: red;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<p class="test">Javascript manipulation: Green when largen than 16px</p>