font size

Hi,
First of all – create your own child theme for Duena and use it for all customizations, because your changes will be lost when the theme is updated, if you modified theme files.
Then use Chrome’s or Mozilla’s firebug to find element you need and rewrite it’s styles in child theme.
For example, with Firebug we can find, that title of the article, it’s <h1 class=”post-title”>, so we add to child theme’s style.css:

.post-title {
   font-size:20px;
}

With this method you can edit almost all CSS.

Add to CSS in your child theme

h1.entry-title {
   font-size: what you need
}