vue.js样式绑定问题

<style>.active {    
    width: 100px;    
    height: 100px;    
    background: green;}</style><p id="app">
  <p v-bind:class="{ active: flag}"></p></p><script>new Vue({
  el: '#app',
  data: {
    flag: true
  }
})
</script>

 v-bind:class="{ active: isActive, 'text-danger': hasError }">

<p id="app">
  <p v-bind:class="classObject"></p></p><script>new Vue({
  el: '#app',
  data: {
    classObject: {
      active: true,      
      'text-danger': true
    }
  }
})
</script>

<p id="app">
    <p v-bind:class="[activeClass, errorClass]"></p></p><script>new Vue({
  el: '#app',
  data: {
    activeClass: 'active',
    errorClass: 'text-danger'
  }
})
</script>

<p id="app">
    <p v-bind:style="{ color: activeColor, fontSize: fontSize + 'px' }">菜鸟教程</p></p><script>new Vue({
  el: '#app',
  data: {
    activeColor: 'green',
    fontSize: 30
  }
})

<p id="app">
  <p v-bind:style="styleObject">菜鸟教程</p></p><script>new Vue({
  el: '#app',
  data: {
    styleObject: {
      color: 'green',
      fontSize: '30px'
    }
  }
})
</script>