i have an issue with my css where if i use margin: 0 instead of margin-top: 0, for header p, the header { margin: 0 0 20px; } will be as good as not there. isit supposed to be like that? if i see what happens in firebug, its because the margin-bottom of header collapsed into the next sibling, the section.

html

<header>
    <h1>ToDo List</h1>
    <p>HTML5 Offline Capable Web Application</p>
</header>

css

header { font: 24px/1em Notethis; color: #666; margin: 0 0 20px; }
header h1 { font: 60px/1.4em Hetilica; margin: 0; }
header p { margin-top: 0; }