Internet browsers offer quite a bit of liberty to people and they customize how it looks if they are bored by the default look. I will explain how to do that for the Firefox browser.
First,click the 3 lines on the top right of the screen right below the X button.
After,click on settings.A new window will pop up. Go to Extensions & Themes.
Another window will open and it will take you to the themes menu.
Currently,the dark theme is selected and there are a couple other default themes that can be selected but if they are not enough you can visit the Firefox store and install new custom themes. For that scroll down and click on “Find more themes”:
Again, another window will open and will take you to the Firefox store where you can search the kind of theme you want by typing some keywords into the search tab.
Select the one you want and install it to your browser.