[Vuejs]-Vue.js binding is hiding parent divs and elements (not intended)

The dash character in your CSS binding makes the name an invalid javascript property name so you need to enclose it in quotes:

v-bind:class="{ 'is-active': isActive }"

I suspect there might be something in your console highlighting this error.

UPDATE

Should have included my jsFiddle showing that your JS and HTML code works if the is-active is wrapped in quotes:

https://jsfiddle.net/psteele/mzjb8wvb/