The simplest way is to just use an image button that looks like you want.
Ok, I may want to use custom toolbar buttons. I've created a couple for testing. How do I edit the skin to use them? This is what i've tried, and it didn't work:
<toolbaritem mode="BtnWithIcon Mode" type="built-in-content" id="1">
Do I need to do more than add the image name? Do I need to remove something?
You must be someone that dearly loves digging into code.
The simplest way to adjust the buttons is to use the built in Skin Editor.
Hmmm, and in writing that response it occurs to me that you haven't exactly advised which of the outputs you are creating. The skin editor I'm referring to is the WebHelp skin editor. To open it, click View > Pods > Project Set-up. Once that pod is open you should see the Skins folder. Expand that and double-click the skin you are using to open and edit it using the skin editor.