[Vuejs]-How do I use multiple templates in one Vuejs project?

As @puddi says, use the <style> tags in your component. What would seem to suit your needs best would be to use scoped style, <style scoped> which means the css you include there only applies to that component, not globally.

Depending on how adventurous you want to get, you could build your project in Nuxt.js (a wrapper for vue) which allows you to define layouts that would do exactly what you’re asking.