Question

How to top margin from first <p> paragraph after <h2>? and if any h2 comes after p then either p should not have bottom margin or h2 should not have top margin

I have

h2
p

h2
p

Answer 1

How to remove top margin from first <p> paragraph after <h2>?

Use this:

h2 + p {
    margin-top: 0;
}

+ is the
adjacent sibling selector. It’s supported in IE7+ and all modern browsers.

if any h2 comes after p then either p should not have bottom margin or
h2 should not have top margin

Using + again in exactly the same way..

p + h2 {
    margin-top: 0;
}

You can even combine them:

h2 + p, p + h2 {
    margin-top: 0;
}