Built in CSS Stylesheet

When Oxygen XML Editor renders content in the Author mode, it adds built-in CSS selectors (in addition to the CSS stylesheets linked in the XML or specified in the document type associated to the XML document). These built-in CSS selectors are processed before all other CSS content, but they can be overwritten in case the CSS developer wants to modify a default behavior.

List of CSS Selector Contributed by Oxygen XML Editor

@namespace oxy "http://www.oxygenxml.com/extensions/author";
@namespace xi "http://www.w3.org/2001/XInclude";
@namespace xlink "http://www.w3.org/1999/xlink";
@namespace svg "http://www.w3.org/2000/svg";
@namespace mml "http://www.w3.org/1998/Math/MathML";

oxy|document {
    display:block !important;
}

oxy|cdata {
    display:-oxy-morph !important;
    white-space:pre-wrap !important;
    border-width:0px !important;
    margin:0px !important;
    padding: 0px !important;
}

oxy|processing-instruction {
    display:block !important;
    color: rgb(139, 38, 201) !important;
    white-space:pre-wrap !important;
    border-width:0px !important;
    margin:0px !important;
    padding: 0px !important;
}

oxy|comment {
    display:-oxy-morph !important;
    color: rgb(0, 100, 0) !important;
    background-color:rgb(255, 255, 210) !important;
    white-space:pre-wrap !important;
    border-width:0px !important;
    margin:0px !important;
    padding: 0px !important;
}

oxy|reference:before,
oxy|entity[href]:before{  
  link: attr(href) !important;
  text-decoration: underline !important;
  color: navy !important;
  
  margin: 2px !important;
  padding: 0px !important;  
}

oxy|reference:before {
  display: -oxy-morph !important;
  content: url(../images/editContent.gif) !important;  
}

oxy|entity[href]:before{
  display: -oxy-morph !important;
  content: url(../images/editContent.gif) !important;
}

oxy|reference,
oxy|entity {
    -oxy-editable:false !important;
    background-color: rgb(240, 240, 240) !important;
    margin:0px !important;
    padding: 0px !important;
}

oxy|reference {
    display:-oxy-morph !important;
    /*EXM-28674 No need to present tags for these artificial references.*/
    -oxy-display-tags: none;
}

oxy|entity {
    display:-oxy-morph !important;
}

oxy|entity[href] {
  border: 1px solid rgb(175, 175, 175) !important;
  padding: 0.2em !important;
}

xi|include {
    display:-oxy-morph !important;
    margin-bottom: 0.5em !important;
    padding: 2px !important;
}
xi|include:before,
xi|include:after{
    display:inline !important;
    background-color:inherit !important;
    color:#444444 !important;
    font-weight:bold !important;
}

xi|include:before {
    content:url(../images/link.gif) attr(href)  !important;
    link: attr(href) !important;
}
xi|include[xpointer]:before {
    content:url(../images/link.gif) attr(href) " " attr(xpointer) !important;
    link: oxy_concat(attr(href), "#", attr(xpointer)) !important;
}

xi|fallback {
    display:-oxy-morph !important;
    margin: 2px !important;
    border: 1px solid #CB0039 !important;
}

xi|fallback:before {
    display:-oxy-morph !important;
    content:"XInclude fallback: " !important;
    color:#CB0039 !important;
}

oxy|doctype {
    display:block !important;
    background-color: transparent !important;
    color:blue !important;
    border-width:0px !important;
    margin:0px !important;
    padding: 2px !important;
}

oxy|error {
    display:-oxy-morph !important;
    -oxy-editable:false !important;
    white-space:pre !important;
    color: rgb(178, 0, 0) !important;
    font-weight:bold !important;
}

oxy|error:before {
    content:url(../images/ReferenceError.png) !important;
}

*[xlink|href]:before {
    content:url(../images/link.gif);
    link: attr(xlink|href) !important;
}


/*No direct display of the MathML and SVG images.*/
svg|svg{	
	display:inline !important;
    white-space: -oxy-trim-when-ws-only;
}
/*EXM-28827 SVG can contain more than one namespace in it*/
svg|svg * {
    display:none !important;
    white-space:normal;
}

mml|math{	
	display:inline !important;
    white-space: -oxy-trim-when-ws-only;
}
mml|math mml|*{
    display:none !important;
    white-space: normal;
}

/*Text direction attributes*/
*[dir='rtl'] { direction:rtl; unicode-bidi:embed; }
*[dir='rlo'] { direction:rtl; unicode-bidi:bidi-override; }

*[dir='ltr'] { direction:ltr; unicode-bidi:embed; }
*[dir='lro'] { direction:ltr; unicode-bidi:bidi-override; }

To show all entities in the Author mode as transparent, without that grayed-out background, first define in your CSS after all imports the namespace:

@namespace oxy "http://www.oxygenxml.com/extensions/author";

and then add the following selector:

oxy|entity {
    background-color: inherit !important;
}