Paragraph Custom Width

Hi good evening
Im trying to reduce the width of some paragraphs to 750 px

–

I have created a custom css like this
.bloque-estrecho{
max-width:750px;
margin: auto;
}

And in my article add it like …
<div class=”bloque-estrecho”>here my text</div>

–

olso try this other css adding p
.bloque-estrecho p{
max-width:750px;
margin: auto;
}
And in my article add it like …
<div class=”bloque-estrecho”><p>here my text</p></div>

–

But not working, could you help me ?
Thanks

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