diff --git a/searx/static/themes/simple/src/less/autocomplete.less b/searx/static/themes/simple/src/less/autocomplete.less
index bfa8e2bc6..0df6fa550 100644
--- a/searx/static/themes/simple/src/less/autocomplete.less
+++ b/searx/static/themes/simple/src/less/autocomplete.less
@@ -1,7 +1,5 @@
 /*! Autocomplete.js v2.6.3 | license MIT | (c) 2017, Baptiste Donaux | http://autocomplete-js.com */
 
-@background_color:  white;
-
 .autocomplete {
   position: absolute;
   max-height: 0;
@@ -11,7 +9,7 @@
   &:active,
   &:focus,
   &:hover {
-    background-color: @background_color;
+    background-color: var(--background_color);
   }
 
   &:empty {
@@ -30,7 +28,7 @@
       &.active,
       &:active,
       &:focus {
-        background-color: @color-base;
+        background-color: var(--color-base);
 
         a:active,
         a:focus,
@@ -47,8 +45,8 @@
 
   &.open {
     display: block;
-    background-color: @background_color;
-    border: 1px solid @color-base;
+    background-color: var(--background_color);
+    border: 1px solid var(--color-base);
     max-height: 500px;
     overflow-y: auto;
     z-index: 100;
@@ -66,7 +64,7 @@
 
   .autocomplete > ul > li {
     padding: 7px 0 7px 10px;
-    border-bottom: 1px solid @color-result-top-border;
+    border-bottom: 1px solid var(--color-result-top-border);
     text-align: left;
   }
 }
diff --git a/searx/static/themes/simple/src/less/definitions.less b/searx/static/themes/simple/src/less/definitions.less
index a3d0de200..4d3d652dc 100644
--- a/searx/static/themes/simple/src/less/definitions.less
+++ b/searx/static/themes/simple/src/less/definitions.less
@@ -4,140 +4,124 @@
  * To change the colors of the site, simple edit this variables
  */
 
-/// Basic Colors
+html {
+  /// Basic Colors
+  --color-base: #3498db;
+  --color-base-dark: #084999;
+  --color-base-light: #ecf0f1;
+  --color-highlight: #094089;
+  --color-black: #000;
 
-@color-base: #3498DB;
-@color-base-dark: #084999;
-@color-base-light: #ECF0F1;
-@color-highlight: #094089;
-@color-black: #000000;
+  /// From autocomplete.less
+  --background_color: white;
 
-///
-@color-error: #db3434;
-@color-error-background: lighten(@color-error, 40%);
+  /// Modal Colors
+  --color-error: #db3434;
+  --color-error-background: lighten(#db3434, 40%);
+  --color-warning: #dbba34;
+  --color-warning-background: lighten(#dbba34, 40%);
+  --color-success: #42db34;
+  --color-success-background: lighten(#42db34, 40%);
 
-@color-warning: #dbba34;
-@color-warning-background: lighten(@color-warning, 40%);
+  /// General Colors
+  --color-font: #444;
+  --color-font-light: #888;
+  --color-red: #25a55b;
+  --color-url-font: #29314d;
+  --color-url-visited-font: #684898;
 
-@color-success: #42db34;
-@color-success-background: lighten(@color-success, 40%);
+  /// Link Colors
+  --color-a-font: var(--color-base);
+  --color-a-font-hover: var(--color-base);
 
-/// General
+  /// Header
+  --color-header-background: #f7f7f7;
+  --color-header-border: #d7d7d7;
 
-@color-font: #444;
-@color-font-light: #888;
+  /// Footer
+  --color-footer-background: #f7f7f7;
+  --color-footer-border: #d7d7d7;
 
-@color-red: #25a55b;
+  /// Search-Input
+  --color-search-border: var(--color-base);
+  --color-search-background: #fff;
+  --color-search-font: #222;
 
-@color-url-font: #29314d;
-@color-url-visited-font: #684898;
+  /// Autocompleter
+  --color-autocompleter-choices-background: #fff;
+  --color-autocompleter-choices-border: var(--color-base);
+  --color-autocompleter-choices-border-left-right: var(--color-base);
+  --color-autocompleter-choices-border-bottom: var(--color-base);
+  --color-autocompleter-choices-font: #444;
+
+  /// Answers
+  --color-answers-border: var(--color-base-dark);
+
+  // Selected
+  --color-autocompleter-selected-background: #444;
+  --color-autocompleter-selected-font: #fff;
+  --color-autocompleter-selected-queried-font: #9fcfff;
+
+  /// Categories
+  --color-categories-item-selected: var(--color-base);
+  --color-categories-item-selected-font: #fff;
+  --color-categories-item-border-selected: var(--color-base-dark);
+  --color-categories-item-border-unselected: #e8e7e6;
+  --color-categories-item-border-unselected-hover: var(--color-base);
+
+  /// Results
+  --color-suggestions-button-background: var(--color-base);
+  --color-suggestions-button-font: #fff;
+  --color-download-button-background: var(--color-base);
+  --color-download-button-font: #fff;
+  --color-result-search-background: var(--color-base-light);
+  --color-result-definition-border: gray;
+  --color-result-torrent-border: lightgray;
+  --color-result-top-border: #e8e7e6;
+
+  // Link to result
+  --color-result-link-font: var(--color-base-dark);
+  --color-result-link-visited-font: var(--color-url-visited-font);
+
+  // Url to result
+  --color-result-url-font: var(--color-red);
+
+  // Publish Date
+  --color-result-publishdate-font: var(--color-font-light);
+
+  // Images
+  --color-result-image-span-background-hover: rgba(0, 0, 0, 0.6);
+  --color-result-image-span-font: #fff;
+
+  // Search-URL
+  --color-result-search-url-border: #888;
+  --color-result-search-url-font: #444;
+
+  /// Settings
+  --color-settings-fieldset: var(--color-base);
+  --color-settings-table-striped: #dbdbdb;
+  --color-settings-tr-hover: #ececec;
+
+  // Labels
+  --color-settings-label-allowed-background: #e74c3c;
+  --color-settings-label-allowed-font: #fff;
+  --color-settings-label-deny-background: #2eee71;
+  --color-settings-label-deny-font: var(--color-font);
+  --color-settings-return-background: var(--color-base);
+  --color-settings-return-font: #fff;
+
+  /// Other
+  --color-engines-font: var(--color-font-light);
+  --color-percentage-div-background: #444;
+}
+
+/// General Size
 @results-width: 45rem;
 @results-offset: 10rem;
 @results-tablet-offset: 0.5rem;
 @results-gap: 5rem;
 @search-width: 40rem;
 
-//
-@color-a-font: @color-base;
-@color-a-font-hover: @color-base;
-
-/// Start-Screen
-
-/// Header
-
-@color-header-background: #f7f7f7;
-@color-header-border: #d7d7d7;
-
-/// Footer
-
-@color-footer-background: #f7f7f7;
-@color-footer-border: #d7d7d7;
-
-/// Search-Input
-
-@color-search-border: @color-base;
-@color-search-background: #FFF;
-@color-search-font: #222;
-
-/// Autocompleter
-
-@color-autocompleter-choices-background: #FFF;
-@color-autocompleter-choices-border: @color-base;
-@color-autocompleter-choices-border-left-right: @color-base;
-@color-autocompleter-choices-border-bottom: @color-base;
-
-@color-autocompleter-choices-font: #444;
-
-/// Answers
-@color-answers-border: @color-base-dark;
-
-// Selected
-@color-autocompleter-selected-background: #444;
-@color-autocompleter-selected-font: #FFF;
-@color-autocompleter-selected-queried-font: #9FCFFF;
-
-/// Categories
-
-@color-categories-item-selected: @color-base;
-@color-categories-item-selected-font: #FFF;
-
-@color-categories-item-border-selected: @color-base-dark;
-@color-categories-item-border-unselected: #E8E7E6;
-@color-categories-item-border-unselected-hover: @color-base;
-
-/// Results
-
-@color-suggestions-button-background: @color-base;
-@color-suggestions-button-font: #FFF;
-
-@color-download-button-background: @color-base;
-@color-download-button-font: #FFF;
-
-@color-result-search-background: @color-base-light;
-
-@color-result-definition-border: gray;
-@color-result-torrent-border: lightgray;
-@color-result-top-border: #E8E7E6;
-
-// Link to result
-@color-result-link-font: @color-base-dark;
-@color-result-link-visited-font: @color-url-visited-font;
-
-// Url to result
-@color-result-url-font: @color-red;
-
-// Publish Date
-@color-result-publishdate-font: @color-font-light;
-
-// Images
-@color-result-image-span-background-hover: rgba(0, 0, 0, 0.6);
-@color-result-image-span-font: #FFF;
-
-// Search-URL
-@color-result-search-url-border: #888;
-@color-result-search-url-font: #444;
-
-/// Settings
-
-@color-settings-fieldset: @color-base;
-@color-settings-table-striped: #dbdbdb;
-@color-settings-tr-hover: #ececec;
-
-// Labels
-@color-settings-label-allowed-background: #E74C3C;
-@color-settings-label-allowed-font: #FFF;
-
-@color-settings-label-deny-background: #2ECC71;
-@color-settings-label-deny-font: @color-font;
-
-@color-settings-return-background: @color-base;
-@color-settings-return-font: #FFF;
-
-/// Other
-
-@color-engines-font: @color-font-light;
-@color-percentage-div-background: #444;
-
 /// Load fonts from this directory.
 @icon-font-path:          "../../../fonts/";
 //** File name for all font files.
diff --git a/searx/static/themes/simple/src/less/preferences.less b/searx/static/themes/simple/src/less/preferences.less
index 3bb04ed6f..c7ba9f979 100644
--- a/searx/static/themes/simple/src/less/preferences.less
+++ b/searx/static/themes/simple/src/less/preferences.less
@@ -73,7 +73,7 @@
 
     & > tbody > tr:nth-child(even) > th,
     & > tbody > tr:nth-child(even) > td {
-      background-color: @color-settings-tr-hover;
+      background-color: var(--color-settings-tr-hover);
     }
   }
 
@@ -83,7 +83,7 @@
   }
 
   .preferences_back {
-    background: none repeat scroll 0 0 @color-settings-return-background;
+    background: none repeat scroll 0 0 var(--color-settings-return-background);
     color: white;
     border: 0 none;
     .rounded-corners;
@@ -95,7 +95,7 @@
 
     a {
       display: block;
-      color: @color-settings-return-font;
+      color: var(--color-settings-return-font);
     }
 
     a::first-letter {
diff --git a/searx/static/themes/simple/src/less/search.less b/searx/static/themes/simple/src/less/search.less
index d10efac24..04a1bef30 100644
--- a/searx/static/themes/simple/src/less/search.less
+++ b/searx/static/themes/simple/src/less/search.less
@@ -5,8 +5,8 @@
 #search {
   padding: 0 2em 0 @results-offset;
   margin: 0;
-  background: @color-header-background;
-  border-bottom: 1px solid @color-header-border;
+  background: var(--color-header-background);
+  border-bottom: 1px solid var(--color-header-border);
 }
 
 #search_wrapper {
@@ -34,19 +34,19 @@
   margin: 0;
   padding: 2px;
   height: 2.2em;
-  background: none repeat scroll 0 0 @color-search-background;
-  border-top: 1px solid @color-search-border;
-  border-bottom: 1px solid @color-search-border;
+  background: none repeat scroll 0 0 var(--color-search-background);
+  border-top: 1px solid var(--color-search-border);
+  border-bottom: 1px solid var(--color-search-border);
   border-right: none;
   border-left: none;
   border-radius: 0;
   outline: none;
-  color: @color-search-font;
+  color: var(--color-search-font);
   font-size: 16px;
   z-index: 10000;
 
   &:hover {
-    color: @color-search-border;
+    color: var(--color-search-border);
   }
 
   &.empty * {
@@ -62,11 +62,11 @@
   margin: 0;
   padding: 2px;
   height: 2.2em;
-  background: none repeat scroll 0 0 @color-search-background;
-  border: 1px solid @color-search-border;
+  background: none repeat scroll 0 0 var(--color-search-background);
+  border: 1px solid var(--color-search-border);
   border-radius: 0;
   outline: none;
-  color: @color-search-font;
+  color: var(--color-search-font);
   font-size: 16px;
   z-index: 2;
 }
@@ -90,8 +90,8 @@
 
   &:hover {
     cursor: pointer;
-    background-color: @color-search-border;
-    color: @color-base-light;
+    background-color: var(--color-search-border);
+    color: var(--color-base-light);
   }
 }
 
@@ -233,9 +233,9 @@
   } */
 
   input[type="checkbox"]:checked + label {
-    background: @color-categories-item-selected;
-    color: @color-categories-item-selected-font;
-    border-bottom: 2px solid @color-categories-item-border-selected;
+    background: var(--color-categories-item-selected);
+    color: var(--color-categories-item-selected-font);
+    border-bottom: 2px solid var(--color-categories-item-border-selected);
   }
 }
 
diff --git a/searx/static/themes/simple/src/less/style.less b/searx/static/themes/simple/src/less/style.less
index d010b9026..920d23c23 100644
--- a/searx/static/themes/simple/src/less/style.less
+++ b/searx/static/themes/simple/src/less/style.less
@@ -41,7 +41,7 @@ html {
   font-size: 0.9em;
   .text-size-adjust;
 
-  color: @color-font;
+  color: var(--color-font);
   padding: 0;
   margin: 0;
 }
@@ -78,8 +78,8 @@ footer {
   padding: 1rem 0;
   width: 100%;
   text-align: center;
-  background-color: @color-footer-background;
-  border-top: 1px solid @color-footer-border;
+  background-color: var(--color-footer-background);
+  border-top: 1px solid var(--color-footer-border);
   overflow: hidden;
 
   p {
@@ -103,8 +103,8 @@ input[type="submit"],
 #results button[type="submit"] {
   padding: 0.5rem;
   display: inline-block;
-  background: @color-download-button-background;
-  color: @color-download-button-font;
+  background: var(--color-download-button-background);
+  color: var(--color-download-button-font);
   .rounded-corners;
 
   border: 0;
@@ -113,13 +113,13 @@ input[type="submit"],
 
 a {
   text-decoration: none;
-  color: @color-url-font;
+  color: var(--color-url-font);
 
   &:visited {
-    color: @color-url-visited-font;
+    color: var(--color-url-visited-font);
 
     .highlight {
-      color: @color-url-visited-font;
+      color: var(--color-url-visited-font);
     }
   }
 }
@@ -134,11 +134,11 @@ article[data-vim-selected]::before {
   padding: 2px;
   content: ">";
   font-weight: bold;
-  color: @color-base;
+  color: var(--color-base);
 }
 
 article.result-images[data-vim-selected] {
-  background: @color-base;
+  background: var(--color-base);
 }
 
 article.result-images[data-vim-selected]::before {
@@ -158,12 +158,12 @@ article.result-images[data-vim-selected]::before {
     margin-bottom: 0;
 
     a {
-      color: @color-result-link-font;
+      color: var(--color-result-link-font);
       font-weight: normal;
       font-size: 1.1em;
 
       &:visited {
-        color: @color-result-link-visited-font;
+        color: var(--color-result-link-visited-font);
       }
 
       &:focus,
@@ -193,7 +193,7 @@ article.result-images[data-vim-selected]::before {
     line-height: 1.24;
 
     .highlight {
-      color: @color-black;
+      color: var(--color-black);
       background: inherit;
       font-weight: bold;
     }
@@ -213,12 +213,12 @@ article.result-images[data-vim-selected]::before {
     padding: 0;
     max-width: 54em;
     word-wrap: break-word;
-    color: @color-result-url-font;
+    color: var(--color-result-url-font);
   }
 
   .published_date {
     font-size: 0.8em;
-    color: @color-result-publishdate-font;
+    color: var(--color-result-publishdate-font);
   }
 
   img {
@@ -228,7 +228,7 @@ article.result-images[data-vim-selected]::before {
       width: 20em;
       min-width: 20em;
       min-height: 8em;
-      // background: @color-base-light;
+      // background: var(--color-base-light);
     }
 
     &.image {
@@ -259,7 +259,7 @@ article.result-images[data-vim-selected]::before {
 
 .engines {
   float: right;
-  color: @color-engines-font;
+  color: var(--color-engines-font);
 
   span {
     font-size: smaller;
@@ -272,7 +272,7 @@ article.result-images[data-vim-selected]::before {
 }
 
 .highlight {
-  color: @color-highlight;
+  color: var(--color-highlight);
   background: inherit;
   font-weight: bold;
 }
@@ -290,12 +290,12 @@ article.result-images[data-vim-selected]::before {
     padding: 0;
     border: none;
     max-height: 200px;
-    background: @color-base-dark;
+    background: var(--color-base-dark);
   }
 
   span a {
     display: none;
-    color: @color-result-image-span-font;
+    color: var(--color-result-image-span-font);
   }
 
   &:hover span a {
@@ -305,7 +305,7 @@ article.result-images[data-vim-selected]::before {
     right: 0;
     padding: 4px;
     margin: 0 0 4px 4px;
-    background-color: @color-result-image-span-background-hover;
+    background-color: var(--color-result-image-span-background-hover);
     font-size: 0.7em;
   }
 }
@@ -342,7 +342,7 @@ article.result-images[data-vim-selected]::before {
 }
 
 .torrent_result {
-  border-left: 10px solid @color-result-torrent-border;
+  border-left: 10px solid var(--color-result-torrent-border);
   padding-left: 3px;
 
   p {
@@ -351,14 +351,14 @@ article.result-images[data-vim-selected]::before {
   }
 
   a {
-    color: @color-result-link-font;
+    color: var(--color-result-link-font);
 
     &:hover {
       text-decoration: underline;
     }
 
     &:visited {
-      color: @color-result-link-visited-font;
+      color: var(--color-result-link-visited-font);
     }
   }
 }
@@ -410,13 +410,13 @@ article.result-images[data-vim-selected]::before {
     font-size: 0.9em;
     display: inline-block;
     background: transparent;
-    color: @color-result-search-url-font;
+    color: var(--color-result-search-url-font);
     cursor: pointer;
   }
 
   input[type="submit"],
   .infobox .url a {
-    color: @color-result-link-font;
+    color: var(--color-result-link-font);
     text-decoration: none;
     font-size: 0.9rem;
 
@@ -447,7 +447,7 @@ article.result-images[data-vim-selected]::before {
 #search_url .title,
 #apis .title {
   margin: 2em 0 0.5em 0;
-  color: @color-font;
+  color: var(--color-font);
 }
 
 #answers {
@@ -547,13 +547,13 @@ article.result-images[data-vim-selected]::before {
   border: 0;
   display: block;
   font-size: 1.2em;
-  color: @color-search-font;
+  color: var(--color-search-font);
 
   a:link *,
   a:hover *,
   a:visited *,
   a:active * {
-    color: @color-search-font;
+    color: var(--color-search-font);
   }
 }
 
@@ -633,7 +633,7 @@ article.result-images[data-vim-selected]::before {
   }
 
   .result {
-    border-bottom: 1px solid @color-result-top-border;
+    border-bottom: 1px solid var(--color-result-top-border);
     margin: 0;
     padding-top: 8px;
     padding-bottom: 6px;
diff --git a/searx/static/themes/simple/src/less/toolkit.less b/searx/static/themes/simple/src/less/toolkit.less
index e9e88e7e0..15f89e1bd 100644
--- a/searx/static/themes/simple/src/less/toolkit.less
+++ b/searx/static/themes/simple/src/less/toolkit.less
@@ -36,15 +36,15 @@ html.js .show_if_nojs {
 }
 
 .danger {
-  background-color: @color-error-background;
+  background-color: var(--color-error-background);
 }
 
 .warning {
-  background: @color-warning-background;
+  background: var(--color-warning-background);
 }
 
 .success {
-  background: @color-success-background;
+  background: var(--color-success-background);
 }
 
 .badge {
@@ -74,7 +74,7 @@ table {
 
   &.striped {
     tr {
-      border-bottom: 1px solid @color-settings-tr-hover;
+      border-bottom: 1px solid var(--color-settings-tr-hover);
     }
   }
 }
@@ -89,7 +89,7 @@ td {
 
 tr {
   &:hover {
-    background: @color-settings-tr-hover;
+    background: var(--color-settings-tr-hover);
   }
 }
 
@@ -104,9 +104,9 @@ tr {
 
 div.selectable_url {
   display: block;
-  border: 1px solid @color-result-search-url-border;
+  border: 1px solid var(--color-result-search-url-border);
   padding: 4px;
-  color: @color-result-search-url-font;
+  color: var(--color-result-search-url-font);
   margin: 0.1em;
   overflow: hidden;
   height: 1.2em;
@@ -173,18 +173,18 @@ div.selectable_url {
 .dialog-error {
   .dialog();
 
-  color: @color-error;
-  background: @color-error-background;
-  border-color: @color-error;
+  color: var(--color-error);
+  background: var(--color-error-background);
+  border-color: var(--color-error);
   .ion-error();
 }
 
 .dialog-warning {
   .dialog();
 
-  color: @color-warning;
-  background: @color-warning-background;
-  border-color: @color-warning;
+  color: var(--color-warning);
+  background: var(--color-warning-background);
+  border-color: var(--color-warning);
   .ion-warning();
 }
 
@@ -253,7 +253,7 @@ div.selectable_url {
   }
 
   & > label:hover {
-    border-bottom: 2px solid @color-categories-item-border-selected;
+    border-bottom: 2px solid var(--color-categories-item-border-selected);
   }
 
   & > section {
@@ -266,9 +266,9 @@ div.selectable_url {
 
   // default selection
   & > label:last-of-type {
-    border-bottom: 2px solid @color-categories-item-border-selected;
-    background: @color-categories-item-selected;
-    color: @color-categories-item-selected-font;
+    border-bottom: 2px solid var(--color-categories-item-border-selected);
+    background: var(--color-categories-item-selected);
+    color: var(--color-categories-item-selected-font);
     font-weight: bold;
     letter-spacing: -0.1px;
   }
@@ -291,14 +291,14 @@ html body .tabs > input:checked {
     color: inherit;
 
     &:hover {
-      border-bottom: 2px solid @color-categories-item-border-selected;
+      border-bottom: 2px solid var(--color-categories-item-border-selected);
     }
   }
 
   + label {
-    border-bottom: 2px solid @color-categories-item-border-selected;
-    background: @color-categories-item-selected;
-    color: @color-categories-item-selected-font;
+    border-bottom: 2px solid var(--color-categories-item-border-selected);
+    background: var(--color-categories-item-selected);
+    color: var(--color-categories-item-selected-font);
   }
 
   + label + section {
@@ -311,7 +311,7 @@ select {
   height: 28px;
   margin: 0 1em 0 0;
   padding: 2px 8px 2px 0 !important;
-  color: @color-search-font;
+  color: var(--color-search-font);
   font-size: 12px;
   z-index: 2;
 
@@ -336,7 +336,7 @@ select {
 
     &:hover,
     &:focus {
-      border-bottom: 1px solid @color-search-border;
+      border-bottom: 1px solid var(--color-search-border);
     }
   }
 }