* finish task #4.

docs/part/basic-typography.md

@@ -15,7 +15,7 @@ filter: paiban pb
   <tbody>
     <tr>
       <th>无衬线字体</th>
-      <td>`"Helvetica Neue", Helvetica, Tahoma, Arial, 'Microsoft Yahei', 'PingFang SC', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif`</td>
+      <td>`@font-family-sans-serif:  "Helvetica Neue", Helvetica, Tahoma, Arial, 'PingFang SC', 'Source Han Sans CN', 'Source Han Sans', 'Source Han Serif', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif;`</td>
     </tr>
     <tr>
       <th>衬线字体</th>

src/less/basic/variables.less

@@ -118,7 +118,7 @@
 // TYPOGRAPHY
 
 // Font family.
-@font-family-sans-serif:  "Helvetica Neue", Helvetica, Tahoma, Arial, 'PingFang SC', 'Source Han Sans CN', 'Source Han Sans', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif;
+@font-family-sans-serif:  "Helvetica Neue", Helvetica, Tahoma, Arial, 'PingFang SC', 'Source Han Sans CN', 'Source Han Sans', 'Source Han Serif', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif;
 @font-family-headings:    @font-family-sans-serif;
 @font-family-serif:       Georgia, "Times New Roman", Times, serif;
 @font-family-monospace:   Monaco, Menlo, Consolas, "Courier New", monospace;

src/less/basic/variables.theme.less

@@ -176,7 +176,7 @@
 // TYPOGRAPHY
 
 // Font family.
-@font-family-sans-serif:  "Helvetica Neue", Helvetica, Tahoma, Arial, 'PingFang SC', 'Source Han Sans CN', 'Source Han Sans', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif;
+@font-family-sans-serif:  "Helvetica Neue", Helvetica, Tahoma, Arial, 'PingFang SC', 'Source Han Sans CN', 'Source Han Sans', 'Source Han Serif', 'Hiragino Sans GB', 'WenQuanYi Micro Hei', sans-serif;
 @font-family-headings:    @font-family-sans-serif;
 @font-family-serif:       Georgia, "Times New Roman", Times, serif;
 @font-family-monospace:   Monaco, Menlo, Consolas, "Courier New", monospace;