:root {
    --tk-primary-color: #000;
    --tk-primary-color-darker: #2d393f;
    --tk-tri-color: #fff;
}

.tk-header h1.tk-title::after,
.tk-summary h3.tk-title::after,
.tk-overview h3.tk-title::after {
    border-bottom: 8px solid var(--tk-tri-color);
}