Custom Post Navigation tweak

Hi there,

you're missing the CSS styling for the custom post nav which is here, the very last rule is what you can change the Next / Previous colors with:

/* CUSTOM POST NAVIGATION - ENSURE GP NAV IS DISABLED */
#post-nav a,
#post-nav .post-nav-wrap {
    -webkit-box-sizing: border-box;
    box-sizing: border-box;
}

#post-nav,
#post-nav .post-nav-wrap {
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
}

#post-nav a {
    -webkit-box-flex: 1;
    -ms-flex: 1 0 50%;
    flex: 1 0 50%;
    box-sizing: border-box;
}

@media (max-width: 768px) {
    #post-nav a {
        -webkit-box-flex: 1;
        -ms-flex: 1 0 100%;
        flex: 1 0 100%;
    }
}

#post-nav .post-nav-wrap {
    background-size: cover !important;
    background-position: center center !important;
    min-height: 120px;
    height: 100%;
    padding: calc(6% + 1em) 5%;
    -webkit-box-shadow: inset 0 -50px 70px 20px rgba(0, 0, 0, 0.5);
    box-shadow: inset 0 -50px 70px 20px rgba(0, 0, 0, 0.5);
    -webkit-transition: -webkit-box-shadow 500ms;
    transition: -webkit-box-shadow 500ms;
    transition: box-shadow 500ms;
    transition: box-shadow 500ms, -webkit-box-shadow 500ms;
    position: relative;
}

#post-nav .post-nav-wrap:hover {
    -webkit-box-shadow: inset 0 -90px 70px 20px rgba(0, 0, 0, 0.5);
    box-shadow: inset 0 -90px 70px 20px rgba(0, 0, 0, 0.5);
}

.post-nav-wrap>* {
    color: #fff;
}

.post-nav-date {
    font-size: 0.9em;
}

.post-nav-title {
    margin: 5px 0 !important;
}

.post-nav {
    min-width: 60px;
    position: absolute;
    top: 0;
    border-radius: 0 0 2px 0;
}

.post-nav:first-child {
    left: 0;
}

.post-nav:last-child {
    right: 0;
}

.post-nav {
    background-color: #ff3366;
    color: #fff !important;
    padding: 5px;
}