change col size of code highlight for mobile phones

src/client/js/components/Admin/Customize/CustomizeHighlightSetting.jsx

@@ -93,7 +93,7 @@ class CustomizeHighlightSetting extends React.Component {
             <h2 className="admin-setting-header">{t('admin:customize_setting.code_highlight')}</h2>
 
             <div className="form-group row">
-              <div className="offset-3 col-6 text-left">
+              <div className="offset-md-3 col-md-6 text-left">
                 <div className="my-0">
                   <label>{t('admin:customize_setting.theme')}</label>
                 </div>
@@ -113,7 +113,7 @@ class CustomizeHighlightSetting extends React.Component {
             </div>
 
             <div className="form-group row">
-              <div className="offset-3 col-6 text-left">
+              <div className="offset-md-3 col-md-6 text-left">
                 <div className="custom-control custom-switch custom-checkbox-success">
                   <input
                     type="checkbox"