[fix] simple theme: set img background color to wallpaper's color

The *background color* of an transparent image is the color of the color of
wallpaper on which all images are shown on.

Set variable `--color-result-image-background` and `--color-base-background` to
the same value.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

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

@@ -68,7 +68,7 @@
   // Images Colors
   --color-result-image-span-background-hover: rgba(0, 0, 0, 0.6);
   --color-result-image-span-font: #fff;
-  --color-result-image-background: #000bbb;
+  --color-result-image-background: #fff;
   /// Settings Colors
   --color-settings-tr-hover: #f7f7f7;
   --color-settings-engine-description-font: darken(#dcdcdc, 30%);
@@ -176,7 +176,7 @@
   // Images Colors
   --color-result-image-span-background-hover: rgba(0, 0, 0, 0.6);
   --color-result-image-span-font: #fff;
-  --color-result-image-background: #8af;
+  --color-result-image-background: #222;
   /// Settings Colors
   --color-settings-tr-hover: #2d2d2d;
   --color-settings-engine-description-font: darken(#dcdcdc, 30%);