Update Tumblr to Reflect Style Guide Changes

[kstack7]

Description
We've recently updated our style guide and need to follow-up by changing existing GDI sites and materials.

Ask
Update Tumblr site (girldevelopit.tumblr.com) to reflect latest style guide changes.

To Do

• Update CSS with proper colors/styles
• Discuss with GDI community
• Eventually push to staging > production

Additional Info
Style guide/brand folder: https://brandfolder.com/gdi