src/css/buttons.css

html[data-theme=dark] .button {
    --ifm-button-border-color: transparent;
}

.button--secondary {
    background-color: var(--ifm-color-primary);
    font-size: 1em;
}

body .button.button--secondary {
    color: var(--ifm-color-white);
    font-size: large;
}