fix: search modal colors

[SethFalco]

Some general amendments to the website:

• Makes the documentation sidebar inline with the table of contents.
• Reduces the shadow in the navbar so it doesn't overlap with the documentation.
• Changes the colors of the search modal to be more cohesive with the rest of the site.
• Change the "Getting Started" button to "Read the docs", so it's clearer that both take the user to the same page.