title: Change styles based on dark or light mode
body: <p>I want to have a dark and a light theme on my Vue app.
  I can create <code>dark.scss</code> file and change classes styles and use <code>!important</code> property to override styles defined in components.
  Or I can use <code>props</code> in my components and change className with <code>v-if</code> based on the theme.
  e.g. set class to <code>className__light</code> when theme is light otherwise set to <code>className__dark</code>.
  which one is better in all situations like performance or time needed to do it? </p>