Text Widget Title

Hi, I have my page as this image shows. I want my Text Widget Title to be bigger than the other title. I tried these code but it doesn’t work for my case.

.widget_headline-widget h1 {
font-size: 20px !important;
}
.widget_headline-widget h3 {
font-size: 16px !important;
}
.widget_text .widget-title {
font-size: 50px important;
}

I’m having Zerif Pro theme, WordPress version 4.6.3, SiteOrigin version 1.7.1.