The subtitles/closed captions settings in YouTube can be adjusted and customized based on user need or preference. Sometimes the default font size of the subtitles or closed captions in a video on YouTube is too small to read by certain users. Some users may want to add a background to the text so the contrast suits their needs. Many customizations are available such as language, font type, size, color, background color, and much more. The video below titled How to Adjust Your Caption Settings on YouTube provides additional details.