A very important part of the desktop customization falls on the different fonts used in different places in the desktop environment.
And not all users like the same fonts. Fortunately in KDE, And in most desktop environments, it’s really easy to change system fonts. In the case of KDE users can change sources which are used in the title bar, toolbar, taskbar, menus, desktop, console (fixed width), and so on.
Changing fonts in KDE
To change the fonts used in the KDE desktop environment we need to go to System Preferences → Appearance of Applications → Fonts.
Once in the section Font type it will be necessary to establish the sources that we wish to use in each part of the environment. This can be done individually or once by clicking on the option Adjust all fonts.
In the section Adjust all fonts we can choose whether we just want to set the type, style or size of the letters, the three options or just two of them. Everything is at the user’s discretion.
Optionally we can enable the smoothed edges and whether or not we want to force the dots per inch.
Once the necessary changes have been made we must apply and accept the modifications. For applications to detect new preferences you will need to restart; for the whole system to detect the changes we will have to log out and log back in.
Learn more – Installing fonts in KDE, Customizing KDE toolbars, Hide KDE title bars