You can create a child of the Striker theme. Create your child theme folder of striker-child. Create a style.css file and place only the following code in the file.
Theme Name: Striker Child
Theme URI: http://www.templateexpress.com/striker-theme/
Author: Ossie Heffell
Author URI: http://www.templateexpress.com/
Description: Striker is a fully responsive and highly customizable WordPress Theme. Add your own logo, header, background, featured areas, social links, pick from 4 different color layouts and much more.
License: GNU General Public License v2.0
License URI: http://www.gnu.org/licenses/gpl-2.0.html
Tags: light, white, one-column, two-columns, right-sidebar, flexible-width, custom-header, custom-menu, featured-images, flexible-header, microformats, post-formats, rtl-language-support, threaded-comments, translation-ready, theme-options, full-width-template, black
This theme, like WordPress, is licensed under the GPL.
Resetting and rebuilding styles have been helped along thanks to the fine work of
Eric Meyer http://meyerweb.com/eric/tools/css/reset/index.html
along with Nicolas Gallagher and Jonathan Neal http://necolas.github.com/normalize.css/
and Blueprint http://www.blueprintcss.org/
Striker WordPress Theme, Copyright 2013 Ossie Heffell
Striker Theme is distributed under the terms of the GNU GPL
Striker Theme based on Underscores (_s) Theme
_s ("Underscores") WordPress Theme, Copyright 2012 Automattic, Inc.
_s ("Underscores") WordPress Theme is distributed under the terms of the GNU GPL
@import url( '../striker/style.css' );
You should already have Striker uploaded to WP.
Upload and activate the striker-child folder containing the style.css file.
Let me know how it goes.