Add missing property for small (#3478)

Also,

* switch to rem
* make the value a little bigger
* move the selectors to utils

Author: XhmikosR

layouts/css/_utils.scss

@@ -29,3 +29,12 @@
 .hidden {
   display: none;
 }
+
+.full-width {
+  width: 100%;
+}
+
+small,
+.small {
+  font-size: .7rem;
+}

layouts/css/styles.scss

@@ -106,14 +106,6 @@ article a {
   }
 }
 
-.full-width {
-  width: 100%;
-}
-
-.small {
-  font-size: 10px;
-}
-
 .color-lightgray {
   color: $light-gray;
 }