If you plan to make larger changes on your website's Design, You'll have to go the child theme way. You need to go to following path:
themes -> default -> assets -> css
and you need to edit file named as:
you can add your design changes into this file and then save and reload your pages to see the effect.
Africa : Zimbabwe, South Africa, Kenya, Tanzania, Nigeria, Egypt | South
Asia : Bangladesh, Bhutan, Maldives, Nepal, Srilanka | South East Asia :Cambodia,
Indonesia, Malaysia, Philippines, Singapore, Thailand, Vietnam | Middle East : Iran,
Jordan, Oman, Qatar, Saudi Arabia, UAE, Yemen, Bahrain, Kuwait, Turkey | Europe : Austria,
Germany, Denmark, Ukraine, Portugal, United Kingdom, Netherlands, Croatia | North America :
United States, Canada, Mexico | Central America : Caribbean Islands, Dominican Republic.