By default, TinyMCE accepts only 20px by 20px icons on the toolbar. If you want the custom toolbar icon to be more than 20 pixels, you will need to edit ui.css in TinyMCE. Edit ui.css ( tiny_mce / themes / advanced / skins / default / ui.css ) and change the following values:
.defaultSkin span.mceIcon, .defaultSkin img.mceIcon {display:block; width:20px; height:20px} .defaultSkin .mceButton {display:block; border:1px solid #F0F0EE; width: 20px; height:20px; margin-right:1px}
Change the width and height as you want.
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