Black density blogger themes
One of the reasons promoted for using themes with dark backgrounds is they save battery life. Less light means less power to view the site with your laptop.
If you are viewing a website on your cell phone at night or outdoors at night, it is far easier for reading the screen when that site is on a black background.
On an emotional level, a black background brings a different tone to the content.
Many black sites use it to emphasise a sense of mystery.
Other non-mainstream sectors use this sense of deepness or darkness to add drama to their content.
In this first example, it adds drama and adventure to a kid's movie. Putting this a white background simply would not have the same effect.

In this next example of a market at night, the colourful lanterns would have nowhere near the same effect as they do. The theme of your site and what you are trying to portray is so important to the design you choose, and how effectively you get your message across.

Elevated Aesthetics and Modern Appeal:
A blog template with a black background can instantly create a visually stunning and modern website. The dark background provides a sleek and sophisticated look that can captivate users and set the tone for an elevated user experience. It also offers a perfect canvas to make vibrant or high-contrast elements, such as images, text, and colors, pop, creating a visually engaging blog.
Focused Content Presentation:
Black backgrounds naturally draw attention to the content displayed on the website. This can be highly beneficial for blogs, where the main focus should be on the articles, images, and media being shared. The black backdrop minimizes distractions, helping users concentrate on the blog's written material and enhancing the overall reading experience. It's especially useful for photographers, artists, and writers who want their visual or written content to stand out prominently.
Reduced Eye Strain and Energy Efficiency:
A black background not only looks stylish but also offers practical benefits. For websites that users are likely to spend a significant amount of time on, such as blogs, a dark background can reduce eye strain and fatigue, especially in low-light conditions. Additionally, on devices with OLED or AMOLED screens, using a black background can help save energy and prolong battery life since individual pixels are turned off in black areas.
However, while black backgrounds can be visually striking and practical in specific contexts, it's essential to consider the target audience, content type, and overall brand identity when choosing a template. Some readers might find dark backgrounds less readable, so a balance between aesthetics and user experience is crucial.