better visualization for contrast checker

[pompydev]

• add a bar like that of GNOME Contrast so users can know how good/bad it is compared to WCAG guideline
• certain color may or may not work depending on the size of the content. Adding different shapes (I recommend including squircle because it is awesome and hexagon because it is the bestagon also it helps users understand how color worlds in rounded and sharp corners), font size and thickness would help greatly.

devtool-plus	GNOME contrast