ui: add margin for titles

No margin-top, because as title tags are contained inside magic-dom divs, all
the margin apply (they are not merged as usual).

Move some colibris rules into the skin independent rules.

src/static/css/iframe_editor.css

@@ -41,6 +41,21 @@ html.inner-editor {
   color: inherit;
 }
 
+#innerdocbody span {
+  line-height: 125%;
+  padding: 6px 0 !important;
+}
+
+option {
+  text-transform: capitalize;
+}
+
+#innerdocbody h1,
+#innerdocbody h2,
+#innerdocbody h3,
+#innerdocbody h4 {
+  margin-bottom: .5em;
+}
 
 /* --------------------- */
 /* -- BROWSER SUPPORT -- */
@@ -52,7 +67,6 @@ body.mozilla, body.safari {
 .safari div {
   padding-right: 1px; /* prevents the caret from disappearing on the longest line of the doc */
 }
-span { line-height: 125%; }
 
 
 /* -------------- */

src/static/skins/colibris/src/pad-editor.css

@@ -6,15 +6,3 @@
   color: #485365;
   color: var(--text-color);
 }
-
-#innerdocbody span {
-  padding: 3px 0 !important;
-}
-
-#innerdocbody h1 span {
-  padding: 0;
-}
-
-option {
-  text-transform: capitalize;
-}