Use cx helper to join class names (#435)

I noticed the class of the input had a trailing space and saw the `cx`
helper function wasn't used there.

Co-authored-by: Ramazan Sancar <ramazansancar4545@gmail.com>

Author: JaZo

src/SearchElement.ts

@@ -38,7 +38,7 @@ export default class SearchElement {
 
     this.form = createElement<HTMLFormElement>(
       'form',
-      ['', classNames.form].join(' '),
+      cx('', classNames.form),
       this.container,
       {
         autocomplete: 'none',
@@ -51,7 +51,7 @@ export default class SearchElement {
 
     this.input = createElement<HTMLInputElement>(
       'input',
-      ['glass', classNames.input].join(' '),
+      cx('glass', classNames.input),
       this.form,
       {
         type: 'text',