docs: fix color contrast to improve DX

[saiponnada]

Fixes #2187

• This PR contains CSS changes
• This PR does not contain CSS changes

Description

Made few CSS changes to improve contrast while reviewing documentation in dark mode.

Notes

Image placeholder's svg might not be visible in dark mode. Checkout the screenshot below. This placeholder svg might need to be replaced in future.

Screenshots

Image Placeholder
Before

After

EEK
Before

After

Menu Button highlight

Before

After

Checklist

• I verify the build is in a non-broken state
• I verify all changes are within scope of the linked issue

• I regenerated all CSS files under dist folder
• I tested the UI in all supported browsers
• I did a visual regression check of the components impacted by doing a Percy build and approved the build
• I tested the UI in dark mode and RTL mode
• I added/updated/removed Storybook coverage as appropriate

[ArtBlue]

If this effort is to fix DX for dark mode, we should use css props for the blue border for the div above too.

Also, for some reason, the Image Placeholder link in the sidebar doesn't take me to the Image Placeholder section though the link and div id seem to match. Weird.

[saiponnada]

Also, for some reason, the Image Placeholder link in the sidebar doesn't take me to the Image Placeholder section though the link and div id seem to match. Weird.

I noticed that. My assumption is it's because the svg also has the same id
<symbol viewBox="0 0 300 300" id="image-placeholder">...</symbol>

[ArtBlue]

Looks good.