如何为父元素样式赋予比子元素样式属性更多的优先级?

I want to edit appearance of an HTML code that i don't know anything about that. for example i just wanna making its text cyan. regardless of it's color. I've tried this:

<p style="color:cyan !important;">
   <span style="color:red;">Hello World</span>
<p>

don't forget this is just an example. I don't really know what will replaced with span tag. imagine this PHP code:

echo '<p style="color:cyan;">';
echo $HTML;// the HTML code that i want to appear in cyan
echo '</p>';

EDIT1: I Can't use Internal and/or External CSS styles.

EDIT2: or give me a PHP solution to remove all color properties from $HTML.

Please refer this fiddle

Following CSS would solve the problem. But is it a proper solution? Probably not.

CSS:

p > * {
    color: cyan !important;
}

Please refer CSS Specificity for more details.

This is an inline style. It has the highest priority.

<p style="color: cyan">Hello World</p>

This is an embedded style. It has the second highest priority.

 <style type="text/css">
 p {color: cyan;}
 </style>

Using an external style sheet (.css file) is the third highest priority.

If you use the span element within the p element, and both have inline styles, the span element will have the higher priority.