Question about some W3C page non-text contrast

I noticed that all of the pages about understanding the various WCAG standards include "Notes" that also are bounded on the left by a green line, and other blocks of text that don't have a similar sub-heading and are bounded by a golden yellow line.
I don't know well enough, but I was looking at this page about understanding minimum contrast requirements<https://www.w3.org/WAI/WCAG21/Understanding/contrast-minimum> and also trying out the TPGi color contrast analyzer. It looks to me like those green and yellow vertical lines marking sections of text, only have contrast ratios of 1.7 and 1.6, respectively.
And, I thought it was odd that the sections of text marked with the yellow lines doesn't have sub-headings to indicate their significance, like the "Note" sub-heading for the text marked with a green line.
Anyhow, I hope that someone who knows it better will check it out. And, I hope to understand the requirements better myself. Thanks!
Brian
Brian Balk
Trainer, Child Support Division
CPACC<https://www.accessibilityassociation.org/cpacccertification>
brian.balk@state.mn.us<mailto:brian.balk@state.mn.us>
(Office) 651-431-4428
Pronouns<https://www.mypronouns.org/>: He/Him/His
Minnesota Department of Human Services
mn.gov/dhs


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