Fix placeholder selector

jet/static/jet/css/_forms.scss

@@ -68,7 +68,7 @@ input[type="text"], input[type="email"], input[type="password"], input[type="url
   transition: background $transitions-duration, box-shadow $transitions-duration, border $transitions-duration;
 
   //noinspection CssInvalidPseudoSelector
-  &:placeholder {
+  &::placeholder {
     color: $input-placeholder-color;
   }
 

jet/static/jet/css/_sidebar.scss

@@ -284,7 +284,7 @@
       margin: 0 0 12px 0;
 
       //noinspection CssInvalidPseudoSelector
-      &:placeholder {
+      &::placeholder {
         color: $sidebar-popup-search-input-placeholder-color;
       }
     }

jet/static/jet/css/_variables.scss

@@ -51,7 +51,7 @@ $sidebar-hover-background-color: #2b3647 !default;
 
 $sidebar-popup-search-input-background-color: #d0dbe6 !default;
 $sidebar-popup-search-input-text-color: #6f7e95 !default;
-$sidebar-popup-search-input-placeholder-color: #d0dbe6 !default;
+$sidebar-popup-search-input-placeholder-color: transparentize(#6f7e95, 0.5) !default;
 
 $sidebar-popup-background-color: #ecf2f6 !default;
 $sidebar-popup-text-color: #6f7e95 !default;

jet/static/jet/css/themes/green/_variables.scss

@@ -45,7 +45,7 @@ $sidebar-hover-background-color: #254d49;
 
 $sidebar-popup-search-input-background-color: #cceae4;
 $sidebar-popup-search-input-text-color: #62a29c;
-$sidebar-popup-search-input-placeholder-color: #cceae4;
+$sidebar-popup-search-input-placeholder-color: transparentize(#6f7e95, 0.5);
 
 $sidebar-popup-background-color: #eff6f5;
 $sidebar-popup-text-color: #62a29c;