<main id="app">
  <header>
    <nav>
      <ul>
        <li 
            v-for="(tab, tabName) in tabs"
            :key="tabName"
            
            >
          <button 
            class="tab" 
            @click="setTabActive(tabName)"
            :class="{'active': tabName === activeTab}"
          >
            <span class="tab-copy">{{ tabName }}</span>
            <span class="tab-background">
              <span class="tab-rounding left"></span>
              <span class="tab-rounding right"></span>
            </span>
          </button>
        </li>
      </ul>
    </nav>
  </header>
  <article>
    <div class="container">
      <transition
        name="fade"
        mode="out-in"
        appear
        :duration="500"
      >
      <tab-content
         v-for="(tabContent, t) in tabs" 
         :data="tabContent"
         :key="'content'+t"
         v-if="t === activeTab"
         inline-template
       >
        <div class="content">
          <h1>{{data.title}}</h1>
          <p>{{data.body}}</p>
          <p>Lorem ipsum dolor sit amet consectetur, adipisicing elit. Nesciunt labore id sint voluptas assumenda optio ullam excepturi officia, a commodi nobis rem saepe error iusto, minima ipsum ducimus quos dignissimos itaque, temporibus esse impedit? Veritatis repellat dolor magnam modi error!
          </p>
        </div>
      </tab-content>
    </transition>
    </div>
  </article>
</main>
body {
  font-family: 'PT Sans', sans-serif;
}

$purple: #8A6CB4;
$pink: #D07FAF;
header {
  background-image: linear-gradient(30deg, $purple, $pink);
  height: 30vh;
  min-height:180px;
  widht: 100%;
  display:flex;
  align-items:flex-end;
  overflow: hidden;
  nav {
    width:100%;
    display:flex;
    justify-content:center;
    border-bottom:20px solid #fff;
    filter: drop-shadow(0 -4px 4px rgba(darken($purple, 30%),.3));
    ul {
      display:flex;
      flex-direction:row;
    }
    .tab {
      $border-radius: 8px;
      $transition-duration:.24s;
      $transition-timing: cubic-bezier(0.86, 0, 0.07, 1);
      font-family: 'PT Sans', sans-serif;
      font-weight: bold;
      font-size: 20px;
      color:#fff;
      border:none;
      padding:16px 40px;
      margin:0 24px 0;
      outline:none;
      cursor:pointer;
      position: relative;
      background:none;
      &:hover {
        .tab {
          &-background {
            height:16px;
          }
          &-rounding {
            transform: scaleY(1);
          }
        }
        
      }
      &.active {
        color:$purple;
        .tab {
          &-background {
            height:100%;
          }
          &-rounding {
            transform: scaleY(1);
          }
        }
        
      }
      &-copy {
        position: relative;
        z-index:1;
      }
      &-background {
        display: block;
        position: absolute;
        bottom: 0;
        left: 0;
        right: 0;
        background: #fff;
        z-index:0;
        height:0;
        border-radius: $border-radius $border-radius 0 0;
        transition: height $transition-timing $transition-duration;
      }
      &-rounding {
        $rounding-size: $border-radius;
        $background-color: #fff;
        //padding:$rounding-size / 2;
        padding:$rounding-size / 2 $rounding-size;
        display: block;
        position:absolute;
        overflow:hidden;
        bottom: 0;
        transform: scaleY(0);
        transform-origin: bottom;
        transition: transform $transition-timing $transition-duration;
        &:before {
          content:"";
          position: absolute;
          width: $rounding-size * 2;
          height: $rounding-size * 2;
          top:-$rounding-size ;
          left:-$rounding-size ;
          border-radius:100%;
        }
        &.left {
          left: -$rounding-size ;
          &:before {
            box-shadow:0 0 0 10rem $background-color;
          }
        }
        &.right {
          right: -$rounding-size ;
          &:before {
            left:$rounding-size;
            box-shadow:0 0 0 10rem $background-color;
          }
        }
      }

    }
  }
}
article {
  .container {
    widht:100%;
    padding: 40px;
    max-width: 1024px;
    box-sizing:border-box;
    margin: 0 auto;
    height:200px;
  }
  h1 {
    font-weight: bold;
    font-size: 48px;
    margin-bottom: 30px;;
    color: $purple;
  }
  p {
    line-height: 1.6;
    font-size: 19px;
    color: rgba(#000,.7);
    margin-bottom: 20px;
  }
}

.fade-enter-active,
.fade-leave-active {
  & > * {
    transition-duration: 200ms;
  transition-property: opacity, transform;
  transition-timing-function: cubic-bezier(.6,.15,.35,.8);
  }
  
}

$delay: 100ms;
$delayStep: 100ms;

.fade-enter,
.fade-leave-to {
  & > * {
    opacity: 0;
    transform: translateY(40px);
  }
}
.fade-enter-active {
  & > * {
    &:nth-child(2) {
      transition-delay: $delay;
    }
    &:nth-child(3) {
      transition-delay: $delay + $delayStep;
    }
  }
}
.fade-leave-active {
  & > * {
    &:nth-child(1) {
      transition-delay: $delay + $delayStep;
    }
    &:nth-child(2) {
      transition-delay: $delay;
    }
  }
}
View Compiled
new Vue({
  el: '#app',
  data: {
    message: 'Hello',
    tabs: {
      'Tab 1': {
        title: 'Awesome Title',
        body: 'Lorem ipsum, dolor sit amet consectetur adipisicing elit. Ab nam alias architecto officia, dolores animi qui debitis incidunt eius temporibus nostrum nihil soluta commodi molestiae necessitatibus ducimus amet. Suscipit, saepe!',
      },
      'Tab 2': {
        title: 'This is great',
        body: 'Lorem ipsasdfasdfasd alias architecto officia, dolores animi qui debitis incidunt eius temporibus nostrum nihil soluta commodi molestiae necessitatibus ducimus amet. Suscipit, saepe!'
      },
      'Tab 3': {
        title: 'Look I\'m a title!',
        body: 'Lorem ipsum, dolor sit amet consectetur adipisicing elit. Ab nam aliasdfasdfaas architecto officia, dolores animi qui debitis incidunt eius temporibus nostrum nihil soluta commodi molestiae necessitatibus ducimus amet. Suscipit, saepe!'
      },
      'Tab 4': {
        title: 'LOREM IPSUM?',
        body: 'Lorem ipsum, dolor sit amet consectetur adipisicing elit. Ab nam alias architecto officia, dolores animi qui debitis incidunt eius temporibus nostrum nihil soluta commodi molestiae necessitatibus ducimus amet. Suscipit, saepe!'
      },
    },
    activeTab: 'Tab 1',
  },
  computed:{
    tabContent() {
      return this.tabs[this.activeTab];
    },
  },
  methods: {
    setTabActive(tab) {
      this.activeTab = tab; 
    }
  },
  components:{
    'TabContent': {
      props: {
        data: Object,
      },
    }
  },
})

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.21/vue.min.js