変更できないスタイルの P 要素があります。新しいフォントサイズを適用するために DIV で囲みたいと思います。内側の P が div の font-size を無視するのはなぜですか?
例:
<html>
<head>
<style>
.para1 { font-size:small; }
</style>
</head>
<div style="font-size:300% !important">
<p class="para1">I must have been asleep, for certainly if I had been fully awake I must have noticed the approach to such a remarkable place. In the gloom the courtyard looked of considerable size, and as several dark ways led from it under great round arches it perhaps seemed bigger than it really is. I have not yet been able to see it by daylight.</p>
</div>
</html>