Button weirdly not clickable

display: initial; is equivalent to display: inline; in your case.

The padding-top is then applied to each line of content, making the second line cover the first line. It is easier to see if you add a background to the containing div.

#div1 {
	padding-top: 15px;
	display: initial;
	background: #f00;
}

<div id="div1">
	<button>
		Button 1
	</button>
	<br>
	<button>
		Button 2
	</button>
</div>