It's Dallas from the Shopify Social Care Team.
All Shopify Checkouts are a locked theme customization file in order to keep your store safe and secure as well as your customer's information. It's locked to merchants, like yourself, as well as Shopify employees, like myself. This means that we won't be able to go into your checkout to make any customizations.
If you go to your Theme Customizer (Online Store > Themes > Customize in your Store Admin) and click on Theme Settings then you will be able to make some minor adjustments by clicking on Checkout.
This isn't exactly the answer that you were looking for I am sure, but there are some features that can be customized so it might be worth taking a look.
If you need assistance with anything else please let me know.
Thank you for your reply!
As you could see from the screenshot attached in my post, I have accessed the checkout page theme settings, however, the only thing I am not finding an option for any where is the 'font colour' for the text mentioned on the checkout page.
The rest of my pages including 'Add to Cart' has a brown font color but only the checkout page is in black which does not look nice. Is there any way I can change using existing options on my dashboard or perhaps by changing the liquid code for it?
I hope I was more clear this time.
Yes, that's what I mean. The only options for the checkout are what you have shared in your image and what I have shared in mine. Since the theme liquid is closed there isn't a way to actually adjust the font color.
I hope that helps to clarify.