Hello Happaerts
Please use CSS to Template Options -> Custom Code -> Custom CSS and it will affect it. Try this CSS to check the effect.
.sp-page-title:after{
content:'';
position:absolute;
left:0;
top:0;
width:100%;
height:100%;
display:inline-block;
background: -moz-linear-gradient(top, rgba(0,47,75,0.5) 0%, rgba(220, 66, 37, 0.5) 100%); /* FF3.6+ */
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(220, 66, 37, 0.5)), color-stop(100%,rgba(0,47,75,0.5))); /* Chrome,Safari4+ */
background: -webkit-linear-gradient(top, rgba(0,47,75,0.5) 0%,rgba(220, 66, 37, 0.5) 100%); /* Chrome10+,Safari5.1+ */
background: -o-linear-gradient(top, rgba(0,47,75,0.5) 0%,rgba(220, 66, 37, 0.5) 100%); /* Opera 11.10+ */
background: -ms-linear-gradient(top, rgba(0,47,75,0.5) 0%,rgba(220, 66, 37, 0.5) 100%); /* IE10+ */
background: linear-gradient(to bottom, rgba(0,47,75,0.5) 0%,rgba(220, 66, 37, 0.5) 100%); /* W3C */
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#002f4b', endColorstr='#00000000',GradientType=0 );
}
Best regards