Show child element on parent hover in CSS

if you have styled hide like this (the page will be displayed as if the element is there but not seen):

#parent .hidden-child{
    visibility: hidden;
}

you may do it like this to just hide it:

#parent:hover .hidden-child{
    visibility: visible;
}

and if you have styled it like this (the page will be displayed as if the element is not there):

#parent .hidden-child{
    display: none;
}

you may do it like this:

#parent:hover .hidden-child{
    display: block;
}

In Action!

#parent {
    width: 10rem;
    height: 10rem;
    background-color: #ababab;
}

#parent .hidden-child{
    visibility: hidden;
}

#parent:hover .hidden-child{
    visibility: visible;
}

<div id="parent">
    <button class="hidden-child">Delete</button>
</div>