[simple] improve styling of subcategory table headers in preferences

searx/static/themes/simple/src/less/definitions.less

@@ -72,6 +72,7 @@
   /// Settings Colors
   --color-settings-tr-hover: #f7f7f7;
   --color-settings-engine-description-font: darken(#dcdcdc, 30%);
+  --color-settings-engine-group-background: #0001;
   /// Detail modal
   --color-result-detail-font: #fff;
   --color-result-detail-label-font: lightgray;
@@ -180,6 +181,7 @@
   /// Settings Colors
   --color-settings-tr-hover: #2d2d2d;
   --color-settings-engine-description-font: darken(#dcdcdc, 30%);
+  --color-settings-engine-group-background: #1a1919;
   /// Toolkit Colors
   --color-toolkit-badge-font: #fff;
   --color-toolkit-badge-background: #777;

searx/static/themes/simple/src/less/preferences.less

@@ -161,6 +161,12 @@
       }
     }
   }
+
+  .engine-group {
+    text-align: left;
+    font-weight: normal;
+    background: var(--color-settings-engine-group-background);
+  }
 }
 
 @media screen and (max-width: @tablet) {

searx/templates/simple/preferences.html

@@ -291,7 +291,7 @@
       </tr>
       {% for group, engines in engines_by_category[categ] | group_engines_in_tab %}
       {% if loop.length > 1 %}
-      <tr><th colspan="9">{{_(group)}}</th></tr>
+      <tr><th colspan="9" class="engine-group">{{_(group)}}</th></tr>
       {% endif %}
       {% for search_engine in engines %}
       {% if not search_engine.private %}