.reveal h1 { font-size: 3em; }

.slides section.has-light-background,
.slides section.has-light-background h1 {
    color: FireBrick;
}

.reveal h6 {
    text-align: center;
    font-style: italic;
    position: fixed;
    bottom: 1px;
    background: rgba(255, 255, 255, 0.05);
    box-shadow: 0px 0px 2px rgba(0, 0, 0, 0.2);
    font-size: 50%;
}


.slides section.has-light-background h6 {
    color: chocolate;
    background: ivory;
}

.reveal pre {
    width: 100%;
    font-size: 0.8em;
}

.reveal h1 { font-size: 3em; }

.slides section.has-light-background,
.slides section.has-light-background h1,
.slides section.has-light-background h2 {
    color: FireBrick;
}

.reveal h6 {
    text-align: center;
    font-style: italic;
    position: fixed;
    bottom: 1px;
    background: rgba(255, 255, 255, 0.05);
    box-shadow: 0px 0px 2px rgba(0, 0, 0, 0.2);
    font-size: 50%;
}


.slides section.has-light-background h6 {
    color: chocolate;
    background: ivory;
}

.reveal pre {
    width: 100%;
    font-size: 0.8em;
}

Change h2 colour on light-coloured slides
Change h2 colour on light-coloured slides
