skouter/grav-admin/user/plugins/admin/themes/grav/scss/simple-fonts.scss

body, h5, h6,
.badge, .note, .grav-mdeditor-preview,
input, select, textarea, button, .selectize-input,
h1, h2, h3, h4,
.fontfamily-sans .CodeMirror pre,
#admin-menu li, .form-tabs > label, .label, {
    font-family: "Helvetica Neue", "Helvetica", "Tahoma", "Geneva", "Arial", sans-serif;
}
//.ck-editor shortcode, .ck-editor twig,
.CodeMirror pre,
code, kbd, pre, samp, .mono  {
    font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace;
}