element-plus/docs/examples/dialog/align-center.vue

<template>
  <el-button text @click="centerDialogVisible = true">
    Click to open the Dialog
  </el-button>

  <el-dialog
    v-model="centerDialogVisible"
    title="Warning"
    width="30%"
    align-center
  >
    <span>Open the dialog from the center from the screen</span>
    <template #footer>
      <span class="dialog-footer">
        <el-button @click="centerDialogVisible = false">Cancel</el-button>
        <el-button type="primary" @click="centerDialogVisible = false">
          Confirm
        </el-button>
      </span>
    </template>
  </el-dialog>
</template>
<script lang="ts" setup>
import { ref } from 'vue'

const centerDialogVisible = ref(false)
</script>
<style scoped>
.dialog-footer button:first-child {
  margin-right: 10px;
}
</style>