[jackie_w]

You can do it by adding a large margin-top to the css for the tag/class you are using for your chapters e.g.

If you view the code in Sigil and your chapter heading look like

<h2>Chapter 1</h2>

then edit the css file to have something like the following (make the 6em bigger/smaller to taste).

h2 {margin-top: 6em;}

If the chapter headings are more like

<h2 class="chaphdg">Chapter 1</h2>

then edit the css file to have something like

.chaphdg {margin-top: 6em;}

or perhaps

h2.chaphdg {margin-top: 6em;}