Fail to make Dolphin Font size bigger

There are General font size,
Fixed width font size,
Small font size,
Which one ? What is each for ? I changed Fixed width font size and applied, however i see no different… does it have to be rebooted to see the effect ?
In order to see the different, i made it 22 size; System Warned me that such big size will make a “weird look” rather use screen scaling for global scaling (this is just like what Jonathan had said) …