Fix Accessibility Violations

[pancakereport]

Follow up to #1

Issues include

• Violation of "image-alt"
• Violation of "color-contrast"
• Violation of "aria-allowed-attr"
• Violation of "scrollable-region-focusable"
• PDF needs to be removed

Alt Text

Alternate Text is required for images. I updated the README to describe how to include alt text and when not doing so is appropriate.

Color Contrast

Color contrast violations appear with the originally selected theme, which I updated to cosmos. It also appears that theme and many other frontmatter options were set multiple times on the page-level, so I removed these in order to let the project-level frontmatter apply. Additionally, color contrast errors appear if code-style is used within a quote (changes made to the Project A1 page).

Aria Allowed Attributes

This violation has to do with callout's. I added a script that will inject role="button"` to fix this.

Scrollable Region Focusable

This violation appears for scrollable regions like wide blocks of code. I added a script that injects tabindex=0 so they are able to be accessed by keyboard users.

Remove PDF

https://ds100.org/debugging-guide/Data-100-Debugging-Guide.pdf