color of the arrowbox

Hi Thomas, since you didn’t provide a link to your site, I couldn’t look at it and used the demo site. I used the web inspector built into my browser and found that the blue color is set as a background in the following CSS rule:

.site-main .post-navigation .nav-previous a, .site-main .paging-navigation .nav-previous a {
    background: #07a1f2;
    color: rgba(255, 255, 255, 0.5);
    float: left;
    padding: 15px 15px 15px 65px;
    position: relative;
    text-align: center;
    width: 50%;
}

If you have not yet done so, I would suggest creating a child theme so that any customizations you make will not be overwritten by a future theme update. Alternately you can use the Edit CSS function in the Jetpack plugin, or use one of the other Custom CSS plugins that will keep CSS changes from being overwritten.

Child Themes
Child Theme creation plugins
Jetpack plugin
Custom CSS plugins

Hi sacredpath,
taht didn’t work for me, your code only changes the fontcolor in my case.
Here is a link to my testsite https://www.hundeschule-owl.de/

br
thomas

To change the background behind the arrow itself, you need to add this rule to your custom CSS as well:

.site-main .post-navigation .meta-nav::before, .site-main .paging-navigation .meta-nav::before {
background: #13f407;
}

Ha, you make my day, works perfekt.

br
thomas