refactor bpk-component-loading-button styles

[mungodewar]

Remember to include the following changes:

• Ensure the PR title includes the name of the component you are changing so it's clear in the release notes for consumers of the changes in the version e.g [KOA-123][BpkButton] Updating the colour
• README.md (If you have created a new component)
• Component README.md
• Tests
• Storybook examples created/updated
• Type declaration (.d.ts) files updated
• For breaking changes or deprecating components/properties, migration guides added to the description of the PR. If the guide has large changes, consider creating a new Markdown page inside the component's docs folder and link it here

[github-actions]

	Warnings
⚠️	Package source files (e.g. packages/package-name/src/Component.js) were updated, but snapshots weren't. Have you checked that the tests still pass?

Browser support

If this is a visual change, make sure you've tested it in multiple browsers.

Generated by 🚫 dangerJS against a1b60e0

[github-actions]

Visit https://backpack.github.io/storybook-prs/3276 to see this build running in a browser.

[github-actions]

Visit https://backpack.github.io/storybook-prs/3276 to see this build running in a browser.

[olliecurtis]

We should also possibly use this as an opportunity to migrate this component to Buttonv2?