[fix] simple theme: /preferences: dark theme version for the response time bar charts

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

@@ -8,6 +8,7 @@
 html {
   /// Base Colors
   --color-base-font: #444;
+  --color-base-font-rgb: 68, 68, 68;
   --color-base-background: #fff;
   --color-url-font: #29314d;
   --color-url-visited-font: #80b;
@@ -108,6 +109,7 @@ html {
   html {
     /// Base Colors
     --color-base-font: #bbb;
+    --color-base-font-rgb: 187, 187, 187;
     --color-base-background: #222;
     --color-url-font: #8af;
     --color-url-visited-font: #96b;

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

@@ -541,8 +541,8 @@ td:hover .engine-tooltip,
 .stacked-bar-chart-median {
   .stacked-bar-chart-base();
 
-  background: @stacked-bar-chart;
-  border: 1px solid fade(@stacked-bar-chart, 90%);
+  background: var(--color-base-font);
+  border: 1px solid rgba(var(--color-base-font-rgb), 0.9);
   padding: 0.3rem 0;
 }
 
@@ -550,7 +550,7 @@ td:hover .engine-tooltip,
   .stacked-bar-chart-base();
 
   background: transparent;
-  border: 1px solid fade(@stacked-bar-chart, 30%);
+  border: 1px solid rgba(var(--color-base-font-rgb), 0.3);
   padding: 0.3rem 0;
 }
 
@@ -558,7 +558,7 @@ td:hover .engine-tooltip,
   .stacked-bar-chart-base();
 
   background: transparent;
-  border-bottom: 1px dotted fade(@stacked-bar-chart, 50%);
+  border-bottom: 1px dotted rgba(var(--color-base-font-rgb), 0.5);
   padding: 0;
 }
 
@@ -566,7 +566,7 @@ td:hover .engine-tooltip,
   .stacked-bar-chart-base();
 
   background: transparent;
-  border-left: 1px solid fade(@stacked-bar-chart, 90%);
+  border-left: 1px solid rgba(var(--color-base-font-rgb), 0.9);
   padding: 0.4rem 0;
   width: 1px;
 }