search: Re-add bootstrap CSS for search input.

This commit re-adds required bootstrap CSS rules for
search box input element.

We also need to add the code to handle dark theme CSS
here to make sure the CSS for dark theme is prioritized
correctly.

web/styles/dark_theme.css

@@ -480,7 +480,8 @@
     select,
     .pill-container,
     .user-status-content-wrapper,
-    #custom-expiration-time-input {
+    #custom-expiration-time-input,
+    #searchbox #search_query {
         background-color: hsl(0deg 0% 0% / 20%);
         border-color: hsl(0deg 0% 0% / 60%);
         color: inherit;

web/styles/search.css

@@ -77,6 +77,11 @@
         overflow: hidden;
         white-space: nowrap;
         padding-left: 35px;
+        color: hsl(0deg 0% 33%);
+
+        &:focus {
+            outline: 0;
+        }
 
         @media (width < $sm_min) {
             vertical-align: text-bottom;