if you want to apply separate css classes for same element with conditions in Vue.js you can use the below given method.it worked in my scenario.
html
<div class="Main" v-bind:class="{ Sub: page}" >
in here, Main and Sub are two different class names for same div element. v-bind:class directive is used to bind the sub class in here. page is the property we use to update the classes when it's value changed.
js
data:{
page : true;
}
here we can apply a condition if we needed. so, if the page property becomes true element will go with Main and Sub claases css styles. but if false only Main class css styles will be applied.