https://github.com/b3log/solo/issues/12658

owmx-3.0/css/base.scss

@@ -29,8 +29,30 @@ Update: 	Dongxu Wang 2011-02-24
 /*
  * skin owmx-3.0 style
  * @author <a href="http://vanessa.b3log.org">Liyuan Li</a>
- * @version 1.1.0.0, Sep 21 2017
-*/
+ * @version 2.0.0.0, Feb 21, 2019
+ */
+
+@import "../../../scss/reset-content";
+.left {
+    float: left;
+}
+
+.right {
+    float: right;
+}
+
+.clear:before,
+.clear:after {
+    display: table;
+    content: "";
+}
+
+.clear:after {
+    clear: both;
+}
+.none {
+    display: none;
+}
 /* Reset */
 header, footer, article, nav, section, aside, time, hgroup {
     display : block;