core/src/scss/components/masthead/_masthead--dark.scss
// Masthead with dark color theme
.su-masthead--dark {
background-color: color(bg--reverse);
.su-lockup__wordmark,
.su-lockup__line1,
.su-lockup__line2,
.su-lockup__line3,
.su-lockup__line4,
.su-lockup__line5 {
color: color(link--reverse);
}
.su-lockup__cell2 {
border-color: color(link--reverse);
}
}