更新组件演示页面，方便用户直接使用组件，去除tn-button的默认背景色，tn-avatar修改参数默认值，修复tn-avatar-group最开始头像进行了偏移、修复无法使用标签的bug，tn-badge修改参数默认值，tn-collapse-item修复背景颜色失效问题，滚动通知移除默认背景颜色和字体大小，tn-count-down修复时间单位不正确问题，列表组件修复背景颜色问题，tn-nav-bar返回按钮修改为可进行修改的图标，tn-step添加点击步骤进行跳转，tn-loading修复默认激活颜色出错问题，tn-tag移除默认背景颜色，优化阴影大小css

libs/components/demo-title.vue

@@ -0,0 +1,90 @@
+<template>
+  <view class="demo-title">
+    <view>
+      <view v-if="type === 'first'" class="main_title">
+        <view v-if="leftIcon" class="main_title__icon main_title__icon--left" :class="[`tn-icon-${leftIcon}`]"></view>
+        <view class="main_title__content">{{ title }}</view>
+        <view v-if="rightIcon" class="main_title__icon main_title__icon--right" :class="[`tn-icon-${rightIcon}`]"></view>
+      </view>
+      <view v-if="type === 'second'" class="second_title">
+        <view class="second_title__content">{{ title }}</view>
+      </view>
+    </view>
+    <view class="content" :class="[{
+      'content--padding': contentPadding
+    }]">
+      <slot></slot>
+    </view>
+  </view>
+</template>
+
+<script>
+  export default {
+    name: 'demo-title',
+    props: {
+      // 标题类型
+      type: {
+        type: String,
+        default: 'first'
+      },
+      // 标题
+      title: {
+        type: String,
+        default: ''
+      },
+      // 左图标
+      leftIcon: {
+        type: String,
+        default: 'star'
+      },
+      // 右图标
+      rightIcon: {
+        type: String,
+        default: 'star'
+      },
+      // 内容容器是否有两边边距
+      contentPadding: {
+        type: Boolean,
+        default: true
+      }
+    }
+  }
+</script>
+
+<style lang="scss" scoped>
+  .main_title {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    margin-top: 50rpx;
+    font-size: 36rpx;
+    font-weight: bold;
+    
+    &__content {
+      padding: 0 18rpx;
+    }
+    
+    &__icon {
+      font-size: 34rpx;
+    }
+  }
+  
+  .second_title {
+    margin: 24rpx 0;
+    margin-left: 30rpx;
+    
+    &__content {
+      font-size: 32rpx;
+      font-weight: bold;
+    }
+  }
+  
+  .content {
+    margin-top: 30rpx;
+    
+    &--padding {
+      margin-left: 30rpx;
+      margin-right: 30rpx;
+    }
+  }
+</style>