Is using camelCase in CSS ids or classes ok or not?

There is one technical limitation if you use camelCase identifiers in your CSS – the |= selector specifier:

<form class="registration"></form>
<form class="search-movies"></form>
<form class="search-actress"></form>

To match only search forms, you can write:

[class|="search"] { font-size: 150% }

You cannot do this with camelCase class names.