Use custom HTML Markup

Hi, I’ve just installed the plugin and the post titles show just fine. But the formatting is off because it inherits the theme’s formatting, not the sidebar formatting. Basically, I would like the ‘Popular posts’ to look just like ‘Recent Posts’, with black text, less space between the lines and more space between the titles.

For ‘Recent posts’ I used the following

.widget-inner a {
    font-weight: normal;
    line-height: 120%;
    font-size: 16px;
}

And I would like to apply the same styling to the ‘Popular posts’. How can I do this? I guess it has something to do with ‘Use custom HTML Markup’, but my CSS knowledge is just not that advanced.

Here’s an URL where the widget appears – travelersuniverse.com/moors-and-christians-festival-alcoy-spain

https://wordpress.org/plugins/wordpress-popular-posts/