모달 창이 사라지지 않고 처음부터 계속 띄어져있어요

<template>
    <div class="inputBox shadow">
        <input type="text" v-model="newTodoItem" placeholder="Type what you have to do"
        v-on:keyup.enter="addTodo">
        <span class="addContainer" v-on:click="addTodo">
            <i class="addBtn fa fa-plus" aria-hidden="true"></i>
        </span>
       
        <Modal> v-if="showModal" @close="showModal = false">
            <h3 slot="header">
                경고!
            </h3>
        </Modal>
    </div>
</template>

<script>
import Modal from './common/Modal.vue'


export default{
    data: function(){
        return {
            newTodoItem:'',
            showModal: false
        }
    },
    methods: {
        addTodo: function(){
            if(this.newTodoItem !== ''){
                this.$emit('addTodoItem', this.newTodoItem);
                this.clearInput(); 
            }else{
                this.showModal = !this.showModal;
            }
        },
        clearInput(){
            this.newTodoItem = '';
        }
    },
    components:{
        Modal: Modal
    }
}
</script>

위에는 TodoInput.vue 부분입니다.

<template>
    <Transition name="modal">
        <div class="modal-mask">
          <div class="modal-wrapper">
            <div class="modal-container">
              <div class="modal-header">
                <slot name="header">default header</slot>
              </div>
    
              <div class="modal-body">
                <slot name="body">default body</slot>
              </div>
    
              <div class="modal-footer">
                <slot name="footer">
                  default footer
                  <button
                    class="modal-default-button"
                    @click="$emit('close')"
                  >OK</button>
                </slot>
              </div>
            </div>
          </div>
        </div>
      </Transition>
</template>


<style>
.modal-mask {
    position: fixed;
    z-index: 9998;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    display: table;
    transition: opacity 0.3s ease;
  }
  
  .modal-wrapper {
    display: table-cell;
    vertical-align: middle;
  }
  
  .modal-container {
    width: 300px;
    margin: 0px auto;
    padding: 20px 30px;
    background-color: #fff;
    border-radius: 2px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.33);
    transition: all 0.3s ease;
  }
  
  .modal-header h3 {
    margin-top: 0;
    color: #42b983;
  }
  
  .modal-body {
    margin: 20px 0;
  }
  
  .modal-default-button {
    float: right;
  }
  
  /*
   * The following styles are auto-applied to elements with
   * transition="modal" when their visibility is toggled
   * by Vue.js.
   *
   * You can easily play with the modal transition by editing
   * these styles.
   */
  
  .modal-enter-from {
    opacity: 0;
  }
  
  .modal-leave-to {
    opacity: 0;
  }
  
  .modal-enter-from .modal-container,
  .modal-leave-to .modal-container {
    -webkit-transform: scale(1.1);
    transform: scale(1.1);
  }

</style>

위에는 Modal.vue 부분입니다.

위는 프로젝트 구조입니다.

모달창이 저렇게 계속 띄어져있습니다. 그냥 실행하자마자 띄어져있고 OK를 눌러도 닫혀지지가 않습니다. 왜 그런지 혹시 알 수 있을까요?