threema-web/src/sass/base/_typography.scss

h1, h2, h3, h4, h5 {
    font-weight: 700;
}
h1 {
    font-size: 2.2em;
}
h2 {
    font-size: 1.5em;
}

html, input, textarea {
    font-family: 'Roboto', "Helvetica Neue", Helvetica, Arial, sans-serif;
}

em {
    font-style: italic;
}

strong {
    font-weight: bold;
}

.text-bold {
    font-weight: bold;
}

.text-italic {
    font-style: italic;
}

.text-strike {
    text-decoration: line-through;
}