Migrate search input color to CSS variable

src/librustdoc/html/static/css/rustdoc.css

@@ -914,6 +914,7 @@ so that we can apply CSS-filters to change the arrow color in themes */
 	font-size: 1rem;
 	width: 100%;
 	background-color: var(--button-background-color);
+	color: var(--search-color);
 }
 .search-input:focus {
 	border-color: var(--search-input-focused-border-color);

src/librustdoc/html/static/css/themes/ayu.css

@@ -40,6 +40,7 @@ Original by Dempfi (https://github.com/dempfi/ayu)
 	--search-result-link-focus-background-color: #3c3c3c;
 	--stab-background-color: #314559;
 	--stab-code-color: #e6e1cf;
+	--search-color: #fff;
 }
 
 .slider {
@@ -149,10 +150,6 @@ details.rustdoc-toggle > summary::before {
 	filter: invert(98%) sepia(12%) saturate(81%) hue-rotate(343deg) brightness(113%) contrast(76%);
 }
 
-.search-input {
-	color: #fff;
-}
-
 .module-item .stab,
 .import-item .stab {
 	color: #000;

src/librustdoc/html/static/css/themes/dark.css

@@ -35,6 +35,7 @@
 	--search-result-link-focus-background-color: #616161;
 	--stab-background-color: #314559;
 	--stab-code-color: #e6e1cf;
+	--search-color: #111;
 }
 
 .slider {
@@ -72,10 +73,6 @@ details.rustdoc-toggle > summary::before {
 	filter: invert(100%);
 }
 
-.search-input {
-	color: #111;
-}
-
 #crate-search-div::after {
 	/* match border-color; uses https://codepen.io/sosuke/pen/Pjoqqp */
 	filter: invert(94%) sepia(0%) saturate(721%) hue-rotate(255deg) brightness(90%) contrast(90%);

src/librustdoc/html/static/css/themes/light.css

@@ -35,6 +35,7 @@
 	--search-result-link-focus-background-color: #ccc;
 	--stab-background-color: #fff5d6;
 	--stab-code-color: #000;
+	--search-color: #000;
 }
 
 .slider {