In case you need to modify the theme’s CSS styles, the fastest way to determine the CSS code you need to apply is using a code inspector tool built into your web browser.
Usually you can display the code inspector (or developer tools) by right clicking the element on the website and choosing “Inspect” from the contextual menu. However, please note that this might differ from browser to browser and some browsers might require installation of additional extension (you may try Firebug for Mozilla Firefox browser).
If you want to learn more on how to work with a code inspector tool, you can take a thorough browser developer tools online course or watch CSS styles specific tool video.
Once you determine the CSS code you can apply it in several ways.