feta(app): add global default flex styles

app.wxss

@@ -7,4 +7,14 @@ page {
   height: 100%;
   width: 100%;
   box-sizing: border-box;
+}
+.ittflex {
+  display: flex;
+  justify-content: center;
+  align-items: center;
+}
+.ittflex-jcs {
+  display: flex;
+  justify-content: flex-start;
+  align-items: center;
 }