feat:重构按钮和icon组件

miniprogram/components3.0/nav-bar/nav-bar.less

@@ -1,4 +1,5 @@
-@import '../../style/theme3.less';
+@import '../../style/theme.less';
+@import '../../assets/fonts/iconfont.less';
 
 .nav-bar {
     position: fixed;
@@ -22,6 +23,21 @@
     box-sizing: border-box;
 }
 
+.nav-bar__back {
+    width: 64rpx;
+    height: 64rpx;
+    display: flex;
+    align-items: center;
+    justify-content: flex-start;
+    flex-shrink: 0;
+}
+
+.nav-bar__back-icon {
+    font-size: 40rpx;
+    color: @color-nav-title;
+    line-height: 1;
+}
+
 .nav-bar__title {
     font-size: @fs-nav-title;
     font-weight: @fw-nav-title;
@@ -41,4 +57,4 @@
 .nav-bar__placeholder {
     width: 100%;
     flex-shrink: 0;
-}
+}