dark iframe fallback

application/Espo/Resources/metadata/themes/Dark.json

@@ -1,6 +1,7 @@
 {
     "stylesheet": "client/css/espo/dark.css",
     "stylesheetIframe": "client/css/espo/dark-iframe.css",
+    "stylesheetIframeFallback": "client/css/espo/hazyblue-iframe.css",
     "dashboardCellHeight": 155,
     "dashboardCellMargin": 19,
     "navbarHeight": 43,

application/Espo/Resources/metadata/themes/DarkVertical.json

@@ -1,6 +1,7 @@
 {
     "stylesheet": "client/css/espo/dark-vertical.css",
     "stylesheetIframe": "client/css/espo/dark-vertical-iframe.css",
+    "stylesheetIframeFallback": "client/css/espo/hazyblue-iframe.css",
     "navbarIsVertical": true,
     "recordTopButtonsStickTop": 61,
     "recordTopButtonsBlockHeight": 21,

client/src/theme-manager.js

@@ -95,6 +95,17 @@ define('theme-manager', [], function () {
             return link;
         },
 
+        getIframeFallbackStylesheet: function () {
+            let link = this.metadata.get(['themes', this.getName(), 'stylesheetIframeFallback']) ||
+                'client/css/espo/espo-iframe.css';
+
+            if (this.config.get('cacheTimestamp')) {
+                link += '?r=' + this.config.get('cacheTimestamp').toString();
+            }
+
+            return link;
+        },
+
         getParam: function (name) {
             return this.metadata.get(['themes', this.getName(), name]) || this.defaultParams[name] || null;
         },

client/src/views/fields/wysiwyg.js

@@ -289,11 +289,17 @@ define('views/fields/wysiwyg', ['views/fields/text', 'lib!Summernote'], function
 
             var body = this.sanitizeHtml(this.model.get(this.name) || '');
 
+            let useFallbackStylesheet = this.getThemeManager().getParam('isDark') && this.htmlHasColors(body);
+
             var linkElement = iframeElement.contentWindow.document.createElement('link');
 
             linkElement.type = 'text/css';
             linkElement.rel = 'stylesheet';
-            linkElement.href = this.getBasePath() + this.getThemeManager().getIframeStylesheet();
+            linkElement.href = this.getBasePath() + (
+                useFallbackStylesheet ?
+                this.getThemeManager().getIframeFallbackStylesheet() :
+                this.getThemeManager().getIframeStylesheet()
+            );
 
             body = linkElement.outerHTML + body;
 
@@ -987,5 +993,17 @@ define('views/fields/wysiwyg', ['views/fields/text', 'lib!Summernote'], function
 
             });
         },
+
+        htmlHasColors: function (string) {
+            if (~string.indexOf('background-color:')) {
+                return true;
+            }
+
+            if (~string.indexOf('color:')) {
+                return true;
+            }
+
+            return false;
+        },
     });
 });

frontend/less/espo/iframe/iframe.less

@@ -13,6 +13,8 @@ body {
     > blockquote:last-child {
         margin-bottom: 0;
     }
+
+    background-color: var(--panel-bg);
 }
 
 body {