class="showAll_dialog" css

<style lang="scss" scoped>
// 修改对话框高度
.showAll_dialog {
  display: flex;
  justify-content: center;
  align-items: center;
  overflow: hidden;

  ::v-deep .el-dialog {
    margin: 0 auto !important;
    height: 80%;
    overflow: hidden;

    .el-dialog__body {
      position: absolute;
      left: 0;
      top: 54px;
      bottom: 0;
      right: 0;
      padding: 0;
      z-index: 1;
      overflow: hidden;
      overflow-y: auto;
      // 下边设置字体，我的需求是黑底白字
      color: #ffffff;
      line-height: 30px;
      padding: 0 15px;
    }
  }
}

</style>

第二种最简单的：

::v-deep .el-dialog {
  height: 78vh;
  overflow: auto;
}