How to give a content editor access to the theme settings?
You could use a hook_form_alter in your custom module.

The following assumes you already have a role called editor existing in your website.


Create a mymodule folder (e.g. in http://www.example.com/sites/all/modules/custom/mymodule)
Create two files in that folder. mymodule.module and mymodule.info
Past the following code in mymodule.module

 &lt;?php

  function mymodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  global $user;

  if ($form_id == 'system_theme_settings' &amp;&amp; in_array('editor', array_values($user-&gt;roles))) {
    // unset the elements you don't want your content editor to have access to
    // unset($form['css3']);
    // Here we want to hide some form elements.
    // To hide/show an element we must use $element['#access'] key in the render array.
    // Using unset($element) might cause issues in form_validate and form_submit processes.
    // So instead of unset($form['css3'], $form['layout']) we set their access to FALSE
    $form['css3']['#access'] = false;
    $form['layout']['#access'] = false;
  }
}

Past the following in mymodule.info

name = Mymodule
core = 7.x
Enable your module at http://www.example.com/admin/modules
Clear your cache


Please note that these are the minimum requirements for creating a custom module and you should definitely read up on best practices for creating custom module at https://www.drupal.org/node/1074360