[Vuejs]-Vue app, styles to html and body elements are not applied, I am using SCSS

Try

* {
  font-size: 62.5% !important;
  color: #777 !important;
}

If there is no other !important styles that should do the trick

It would be better if you give a class to your body tag and apply your style to a class rather than applying directly to an element tag.

Or even better if you set a main div under body tag, give it a class and style that instead:

// app.vue
<template>
  <div id="app">
    <div class="bodyContainer">
      //Content
    </div>
  </div>
</template>


// main.scss    
.bodyContainer {
  font-size: 62.5%;
  color: #777;
}