With margins

Be a display block
Must have a set width
Margin left/right: auto (both)
- If the values of margin-left and margin-right are both auto, the calculated space is evenly distributed

Text align

Works on all inline elements

<div class="btn-parent">
	<button class="btn">Google Search</button>
	<button class="btn">I'm Feeling Lucky</button>
</div>

.btn-parent {
    text-align: center;
}
 
.btn {
    margin-top:30px;
    display:inline;
    background: #dfe1e5;
    border: none;
    border-radius: 5px;
    padding: 8px;
    padding-left: 13px;
    padding-right: 13px;
}

text-align should be applied in the parent

Flexbox!

CSS Flexbox