docs #2821: fix writing mistakes in letter case

[xiaodong2008]

Description of Problem

Some letters should be capitalised, check below:

+ <button>Click Me</button>
+ <h1>Title</h1>
+ <p>This is a paragraph or sentence</p>
+ <p>Count: 0</p>
- <p>short text/word</p> // no need to capitalised

Refers to #2821

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[bencodezen]

Thanks for the PR @xiaodong2008! I agree with most of the casing changes, but removing the is in the examples isn't related to letter casing and arguably is better as is since it is more explicit as a statement.

Once you remove those changes, I'm happy to approve and merge these changes!

[bencodezen]

Thanks for the PR @xiaodong2008!