If you're just interested in increasing the font size of just the first paragraph of any document, an effect used by online publications, then you can use the first-child pseudo-class to achieve the desired effect.
p:first-child
{
font-size: 115%; // Will set the font size to be 115% of the original font-size for the p element.
}
However, this will change the font size of every p element that is the first-child of any other element. If you're interested in setting the size of the first p element of the body element, then use the following:
body > p:first-child
{
font-size: 115%;
}
The above code will only work with the p element that is a child of the body element.
remas scale for your font size for more flexibility and it's more dynamic.