Titan Embeds has a selection of pre-built themes you may use for your embed. These themes are fully compatible with custom CSS and approved by Titan's developers. As of August 2018, these themes include:

You can select a theme for your embed by using the theme query parameter. It's used as follows: theme=<ThemeName>. You have to replace <ThemeName> with the name of the theme you would like to use, for example: theme=FireWyvern. Query parameters get appended to the end of your embed's URL like so:


You may demo this here. The Fire Wyvern theme is used in this instance, but you may replace the theme query parameter's value with another one to see what you like.