MAGETWO-86867: [Tech Debt] Revise LESS/CSS classes and icons

Author: irenelagno

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/_preview.less

@@ -602,7 +602,7 @@
                     display: inline-block;
 
                     a {
-                        color: white;
+                        color: @color-white;
                         display: block;
                         font-size: 13px;
                         line-height: 42px;

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/button-item/_default.less

@@ -9,13 +9,13 @@
 
 .pagebuilder-content-type {
     .pagebuilder-button-item {
-        font-size: 0;
-        width: auto;
         [contenteditable=true] {
             display: inline-block;
             min-height: 18px;
             min-width: 20px;
         }
+        font-size: 0;
+        width: auto;
         .pagebuilder-options {
             bottom: 0;
             left: calc(50% - 5px);