There's beneath every title a short thick underline and a thin bottom-border accross the entire page.

Can I remove these ? Can't find it in the styles customizer ...

Hi there,
add this code to your css/custom.css

h1.uk-article-title::after, h3.uk-panel-title::after {
background: none;
}

h1.uk-article-title, h3.uk-panel-title {
border: none;
}

www.joomlaplates.com/support/documentation/custom-css-in-joomla