Button spacing desktop vs mobile

I have the buttons under our logo aligned and centered on desktop, how can do the same for mobile? They appear on two separate lines on mobile.

Add to Design > Custom CSS

@media screen and (max-width:640px) {
div#block-yui_3_17_2_1_1674347250860_9277+.row .span-6 {
    width: 50% !important;
    float: left !important;
}
}