ui: prism: 支持显示空白符

packages/ui-default/components/highlighter/highlighter.page.styl

@@ -120,3 +120,32 @@ pre > code
         display: block
         padding-right: 0.8em
         text-align: right
+
+.token.tab:not(:empty),
+.token.cr,
+.token.lf,
+.token.space
+	position: relative
+
+.token.tab:not(:empty):before,
+.token.cr:before,
+.token.lf:before,
+.token.space:before
+	color: #808080
+	opacity: 0.6
+	position: absolute
+
+.token.tab:not(:empty):before
+	content: '\21E5'
+
+.token.cr:before
+	content: '\240D'
+
+.token.crlf:before
+	content: '\240D\240A'
+
+.token.lf:before
+	content: '\240A'
+
+.token.space:before
+	content: '\00B7'