too much space betwen post title and post text

Your DOM elements have vartical margin and padding.

Change this:

h2.pagetitle {
margin:0 0 5px;
padding:8px 8px 8px 15px;
}

#content .postcontent {
padding:15px 15px 0;
}

To this:

h2.pagetitle {
margin:0;
padding:8px 8px 0 15px;
}

#content .postcontent {
padding:0 15px;
}

Then, a large space will disappear.