An example of positioning the full-width slider text at the lower-left hand side of the module's content area. Don't forget mobile! Set something at least at the 768px break point.
.et_pb_fullwidth_slider_0 .et_pb_slide_description {
text-align: left;
padding-top: 25% !important;
padding-bottom: 7% !important;
margin-left: -20%;
width: 70%;
}