点击选项一，选项一变色

点击选项二，选项二变色

<template>
  <div id="app">
    <div>
      <span @click="select(1)" :class="index ==1?'blue':'gery'">选项一</span>
      <span @click="select(2)" :class="index ==2?'blue':'gery'">选项二</span>
      <span @click="select(3)" :class="index ==3?'blue':'gery'">选项三</span>
    </div>
  </div>
</template>
<script>
export default {
  data() {
    return {
      index: 1,
    };
  },
  methods: {
    select(i) {
      this.index = i;
    },
  },
};
</script>

<style>
.gery {
  color: grey;
  font-size: 20px;
}
.blue {
  color: blue;
  font-size: 30px;
}
</style>