PLT-5985 Cleaned up CSS for post textbox (#5974)

webapp/components/textbox.jsx

@@ -246,6 +246,14 @@ export default class Textbox extends React.Component {
             </div>
         );
 
+        let textboxClassName = 'form-control custom-textarea';
+        if (this.props.emojiEnabled) {
+            textboxClassName += ' custom-textarea--emoji-picker';
+        }
+        if (this.state.connection) {
+            textboxClassName += ' ' + this.state.connection;
+        }
+
         return (
             <div
                 ref='wrapper'
@@ -254,7 +262,7 @@ export default class Textbox extends React.Component {
                 <SuggestionBox
                     id={this.props.id}
                     ref='message'
-                    className={`form-control custom-textarea${this.props.emojiEnabled ? '-emoji' : ''} ${this.state.connection}`}
+                    className={textboxClassName}
                     type='textarea'
                     spellCheck='true'
                     placeholder={this.props.createMessage}