Integrate light theme's `low-sat-blue-dark` using a media query

public/css/icinga/base.less

@@ -123,6 +123,7 @@
     --menu-flyout-color: #535353;
 
     --low-sat-blue: #DEECF1;
+    --low-sat-blue-dark: #c0cccd;
   }
 }
 

public/css/icinga/main.less

@@ -94,7 +94,7 @@ a:hover > .icon-cancel {
   padding: 0.25em 0.5em;
 
   &:hover {
-    background: @low-sat-blue-dark;
+    .var(background, low-sat-blue-dark);
     text-decoration: none;
   }
 }

public/css/themes/icinga-light-theme.less

@@ -4,5 +4,3 @@
 @gray-light: #C9C9C9;
 @gray-lighter: #EEEEEE;
 @gray-lightest: #F7F7F7;
-
-@low-sat-blue-dark: #c0cccd;