Rename `simple-search.scss` to match component name

 - Rename `simple-search.scss` and the CSS classes it defines to match
   the name of the module which defines the component structure and
   logic
 - Remove reference to `simple-search-inactive` CSS class which did not
   exist

src/sidebar/components/search-input.js

@@ -44,16 +44,9 @@ function SearchInput({ alwaysExpanded, query, onSearch }) {
   }
 
   return (
-    <form
-      className={classnames(
-        'simple-search-form',
-        !query && 'simple-search-inactive'
-      )}
-      name="searchForm"
-      onSubmit={onSubmit}
-    >
+    <form className="search-input__form" name="searchForm" onSubmit={onSubmit}>
       <input
-        className={classnames('simple-search-input', {
+        className={classnames('search-input__input', {
           'is-expanded': alwaysExpanded || query,
         })}
         type="text"
@@ -67,7 +60,7 @@ function SearchInput({ alwaysExpanded, query, onSearch }) {
       {!isLoading && (
         <button
           type="button"
-          className="simple-search-icon top-bar__btn"
+          className="search-input__icon top-bar__btn"
           onClick={() => input.current.focus()}
         >
           <i className="h-icon-search"></i>

src/styles/sidebar/components/simple-search.scss → src/styles/sidebar/components/search-input.scss

 @import "../../base.scss";
 @import "../../mixins/icons";
 
-.simple-search-form {
+.search-input__form {
   display: flex;
   flex-flow: row nowrap;
 
@@ -9,18 +9,18 @@
   color: $gray-dark;
 }
 
-.simple-search-icon {
+.search-input__icon {
   order: 0;
 }
 
-:not(:focus) ~ .simple-search-icon {
+:not(:focus) ~ .search-input__icon {
   color: $gray-light;
 }
 
 @at-root {
   $expanded-max-width: 150px;
 
-  .simple-search-input {
+  .search-input__input {
     @include outline-on-keyboard-focus;
 
     flex-grow: 1;

src/styles/sidebar/sidebar.scss

@@ -41,8 +41,8 @@ $base-line-height: 20px;
 @import './components/search-status-bar';
 @import './components/selection-tabs';
 @import './components/share-link';
+@import './components/search-input';
 @import './components/sidebar-tutorial';
-@import './components/simple-search';
 @import './components/svg-icon';
 @import './components/spinner';
 @import './components/tags-input';