fix($theme-default): improve last-updated text color contrast

[cyrilf]

Summary

On the .last-updated .time element, the color contrast is too low which raised an accessibility warning in a Lighthouse report.

Here is a minor tweak of the color to fix that.

It won't affect much the end user, but provides:

• a more accessible website 🎉
• a better lighthouse accessibility score by default 👌

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:
  Style

If changing the UI of default theme, please provide the before/after screenshot:

	Before	After
Screenshot
Chrome contrast ratio

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

You have tested in the following browsers: (Providing a detailed version will be better.)

• Chrome
• Firefox
• Safari
• Edge
• IE

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

If we want to support a contrast ratio AAA we would need to update the color to at least: #595959. But the end result doesn't work as the time seems as black as the text. That's why, going for a contrast ratio AA is sufficient.

[billyyyyy3320]

Thanks! I changed the title since we use style as code style update.

[cyrilf]

Yes ok, got it! 👍

[Mister-Hope]

#2301 has adjust the color.

See here

Do you think it's still light now?

[cyrilf]

@Mister-Hope yep, on your PR the contrast is still too low to reach the accessibility standard.

If you use Chrome, simply open the dev tools, find the color in the css and click on the colored square. You'll see the contrast ratio (that you can expend) and see if it matches the minimum ratio. (as in the above screenshot)

So the minimum value is still #767676 and my PR still applies.
Your --light-grey should be of this value minimum.

[Mister-Hope]

Thanks, I will make a commit later.

[meteorlxy]

@newsbielt703 I prefer to take this PR as a perf or fix 🤔

[billyyyyy3320]

@meteorlxy Yeah it should be.