Uppercase.vue

// Uppercase.vue
<template>
  <div>
    <slot v-bind="{style: style}" />
  </div>
</template>

<script>
export default {
  data() {
    return {
      style: {
        textTransform: 'uppercase'
      }
    }
  }
}
</script>

// App.vue
<app>
  <uppercase>
    <template slot-scope="attrs">
      <span :style="attrs.style">
        hello world
      </span>
    </template>    
  </uppercase>
</app>