Migrate to styled-components

[Niyousha99]

We are currenly following the old approach of using css stylesheets which is not ideal for global scope and dynamic styling. After some investigation, it would be more beneficial for our project to migrate to styled-components, for meeting the previously mentioned requirements as well as creating a reusable design system with theming and using SASS syntax.

I propose we start with migrating our smallest components whose styling scope changes won't largely affect other areas in code.

[Niyousha99]

Remaining css modules to convert to styled components:

• App.css
• HomePage.css
• Team.css (TODO as part of Redesign Team section on mobile view  #297)
• DocsPage.css
• GuidesSection.css
• ApplyPage.css
• FeaturedProject.css
• Blobbie.css (low priority)
• Navbar.css
• NumberStat.css

[Niyousha99]

Rest of work will be covered in #494