diff --git a/core/upgrade/index.php b/core/upgrade/index.php
index f9ed6c7c77..eb56ed9fce 100644
--- a/core/upgrade/index.php
+++ b/core/upgrade/index.php
@@ -221,12 +221,12 @@
 				}
 			}
 			echo "<button type='button' class='btn btn-default' style='float: right;' onclick=\"$('#source_preview_layer').fadeOut(200);\">".$text['button-close']."</button>\n";
-			echo "<b>".$text['header-source_code_upgrade_preview']."</b>\n";
+			echo "<div class='title'>".$text['header-source_code_upgrade_preview']."</div>\n";
 			echo "<br><br>\n";
 			if (!empty($response) && is_array($response)) {
 				echo str_replace('APP_NAME', (!empty($_GET['title']) ? "<strong>".$_GET['title']."</strong>" : null), $text['description-source_code_changes_found']);
 				echo "<br><br><br>\n";
-				echo "<div style='width: 100%; max-height: 250px; overflow: auto; border: 1px solid ".($_SESSION['theme']['table_row_border_color']['text'] ?? '#c5d1e5')."; padding: 12px 15px; background-color: ".($_SESSION['theme']['table_row_background_color_light']['text'] ?? '#fff')."; font-family: monospace; font-size: 85%; color: green;'>\n";
+				echo "<div class='file_paths'>\n";
 				if (!empty($response) && is_array($response)) {
 					echo implode("<br>\n<hr style='margin: 3px 0;'>\n", $response);
 				}
@@ -254,35 +254,6 @@
 	require_once "resources/header.php";
 
 //source preview layer
-	echo "<style>\n";
-	echo "	#source_preview_layer {\n";
-	echo "		z-index: 999999;\n";
-	echo "		position: absolute;\n";
-	echo "		left: 0px;\n";
-	echo "		top: 0px;\n";
-	echo "		right: 0px;\n";
-	echo "		bottom: 0px;\n";
-	echo "		text-align: center;\n";
-	echo "		vertical-align: middle;\n";
-	echo "		}\n";
-	echo "	#source_preview_container {\n";
-	echo "		display: block;\n";
-	echo "		overflow: auto;\n";
-	echo "		background-color: #fff;\n";
-	echo "		padding: 25px 25px;\n";
-	if (http_user_agent('mobile')) {
-		echo "	margin: 0;\n";
-	}
-	else {
-		echo "	margin: auto 10%;\n";
-	}
-	echo "		text-align: left;\n";
-	echo "		-webkit-box-shadow: 0px 1px 20px #888;\n";
-	echo "		-moz-box-shadow: 0px 1px 20px #888;\n";
-	echo "		box-shadow: 0px 1px 20px #888;\n";
-	echo "		}\n";
-	echo "</style>\n";
-
 	echo "<div id='source_preview_layer' style='display: none;'>\n";
 	echo "	<table cellpadding='0' cellspacing='0' border='0' width='100%' height='100%'>\n";
 	echo "		<tr>\n";
diff --git a/themes/default/css.php b/themes/default/css.php
index 5437f172ed..c3f0b40cb4 100644
--- a/themes/default/css.php
+++ b/themes/default/css.php
@@ -3854,6 +3854,52 @@ else { //default: white
 		text-align: left;
 		}
 
+/* UPGRADE - SOURCE CODE PREVIEW ************************************************/
+
+	#source_preview_layer {
+		z-index: 999999;
+		position: absolute;
+		left: 0px;
+		top: 0px;
+		right: 0px;
+		bottom: 0px;
+		text-align: center;
+		vertical-align: middle;
+		}
+
+	#source_preview_container {
+		display: block;
+		overflow: auto;
+		background-color: <?=$modal_background_color?>;
+		padding: 25px 25px;
+		margin: auto 10%;
+		text-align: left;
+		box-shadow: <?=$modal_shadow?>;
+		border-radius: <?=$modal_corner_radius?>;
+		color: <?=$modal_message_color?>;
+		}
+
+	#source_preview_container div.title {
+		display: block;
+		font-weight: bold;
+		font-size: 120%;
+		font-family: <?=$modal_title_font?>;
+		color: <?=$modal_title_color?>;
+		text-align: <?=$modal_title_alignment?>;
+		margin: <?=$modal_title_margin?>;
+		}
+
+	#source_preview_container div.file_paths {
+		width: 100%;
+		max-height: 250px;
+		overflow: auto;
+		border: 1px solid <?=$table_row_border_color?>;
+		padding: 12px 15px;
+		background-color: <?=$table_row_background_color_light?>;
+		font-family: monospace; font-size: 85%;
+		color: green;
+		}
+
 /* ACE EDITOR *******************************************************************/
 
 	div#editor {