Why Css text-transform capitalize not working?

Capitalize only affects the first letters of words. It will not change the case of the rest of the letters in a word. For example, if you capitalize a word that's in all capital letters already, the other letters in the word won't switch to lowercase. This is nice when your text includes an acronym or abbreviation that shouldn't include any lowercase letters.

If you change your provided text to lowercase, you will see it work just fine!

But to be answer complete, i will try to find a way to capitalize with the desired way no matter the input.

Seems it is not possible with CSS only, for something beside a single word text if you are not wrapping every word in a different element.

Single word snippet

span,
a,
h2 {
   text-transform:lowercase
}

span:first-letter,
a:first-letter,
h2:first-letter {
  text-transform: capitalize;
}

CSS text-transform: capitalize will only affect the first character.

According to the specs:

capitalize Puts the first character of each word in uppercase; other characters are unaffected.

I strongly suggest to just have the content edited. Remember that at the end of the day, technologies such as css is just 1 way to solve the problem. The better solution, again, would be to edit that content and capitalize it, whether it be stored in the database or just static content in the markup.

As a hack (if you really want to use a code-level solution), you can use JavaScript to transform all letters first into lowercase. Then use /\b(\w)/g to match the instances of first letters, then use toUpperCase() on each

document.querySelector("a").innerText = document.querySelector("a").innerText.toLowerCase().replace(/\b(\w)/g, x => x.toUpperCase());

<h2><a class="ml-5 mt-5 d-block" href="#">IT IS AN EXAMPLE TEXT IN HREF</a></h2>