Escape CSS class names

CSS class names can't contain the : character. For example, it's not possible to declare the following class in CSS:
.lg:flex {
    ...
}
However we can use the \ character to correct it:
.lg\:flex {
    ...
}
The class name is usable in HTML as usual:
<div class="lg:flex">    ...</div>
Using \ to escape CSS class names has been used a lot in some CSS frameworks such as Tailwind.