20px is coming from line 1172 –
.slider .wrap {
margin: 0 auto 20px;
padding: 0;
width: 1140px;
}
And the other 20px is coming from line 1178 –
.slider .widget {
margin: 0 0 20px;
}
You can change the margin on both of those sections to margin: 0;
if you’re not going to be using more than one widget inside of the slider area.