What is this syntax in css?

Question

css

<ul id="my-listbox"
                class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu"
                style="[if state.expanded]display:block[else]display:none[endif];">
</ul>

conditions are used in the style attribute, where can I learn and read about this syntax?

Answer 1

Conditional CSS is no longer being maintained.