How to remove default style of header in wordpress metabox

I have the problem which when I create a header in my wordpress plugin metabox, it always apply the default style on my header:
enter image description here

even when I apply, my own style, <h3 style="background-color: black; color:blue">Text Block Settings</h3>, it only changes the text color but not the background color, why??
enter image description here

Related posts

Leave a Reply