Errors on plugin code

After activating on settings page these errors show up:

Undefined index: myfixed_cssstyle	1	
-
get_header()
wp-content/themes/child/index.php:17
locate_template()
wp-includes/general-template.php:41
load_template('wp-content/themes/child/header.php')
wp-includes/template.php:671
wp_head()
wp-content/themes/child/header.php:21
do_action('wp_head')
wp-includes/general-template.php:2745
MyStickyMenuFrontend->mysticky_build_stylesheet_content()
wp-includes/class-wp-hook.php:286
wp-content/plugins/mystickymenu/mystickymenu.php:635