simple-icons/_sass/_elements.scss

* {
    box-sizing: border-box;
}

:root {
    font-size: 100%;
}

a {
    text-decoration: none;
}

body {
    background-color: $color-white;
    color: $color-black;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
    font-size: 0.875rem;
    line-height: 1.5rem;
    margin: 0;
}