Use admin theme colors, instead of hardcoded ones

[PanosSynetos]

I've been working on harmonizing all the different pink colors, and using admin theme colors

• pdqkbG-2Tq-p2#comment-1471
• Fix hardcoded admin colors, use admin theme colors woocommerce/woocommerce#39182

I noticed that this plugin has some hardcoded colors

wp-admin/admin.php?page=wc-settings&tab=shipping&section=woocommerce-services-settings

I didn't go through all the different colors in the plugin, but at least the above two screens could benefit from changing the colors to var(--wp-admin-theme-color) or var(--wp-admin-theme-color-darker-10)

The color changes introduced in PR woocommerce/woocommerce/pull/39182 will be released in WC 8.1