docs: change capitalization for css hex color values

[sreevani-ship-it]

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• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
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PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[x] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

inconsistent capitalization of css hex color values.
Issue Number: 23113 #23113

What is the new behavior?

changed hex color values from uppercase to lowercase and used 3 character hexadecimal notation where possible.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[mary-poppins]

You can preview 159d7e6 at https://pr23511-159d7e6.ngbuilds.io/.

[jainanuj0812]

As per the discussion over the issue thread, I don't think it is approved or required.

And if these changes requested to be pushed, it should be changed globally and not in these particular files.

[jenniferfell]

Did some characters get dropped accidentally? CFD8DC seems to be a medium gray, and CFD seems to be a bright green.

[sreevani-ship-it]

I followed hex code style recommendation and reduced it to 3 digits. But on a second look, the RGB values are different when it is 3 digits. Reverted it back to 6 digit code.

[gkalpak]

3-digit hex color values are equivalent to 6-digit color values with each digit duplicated. I.e. #cfd is the same as #ccffdd, which is indeed quit different than #cfd8dc (in 6-digit hex color values each digit pair corresponds to one of R, G, B).

[jenniferfell]

@IgorMinar On the associated issue, @jelbourn comments that the Google style is lowercase.

[alfaproject]

Double space after colon

[gkalpak]

I haven't checked if there are more, but the changes on this PR lgtm.

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[IgorMinar]

I fixed the extra ws issue and pushed to this PR. lgtm now.

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