Hi Chaimongkol,
To change the font family of your own for widget-title. First Go to Appearance -> Theme Options/Customize -> Webmaster Tools -> Analytics
and paste your font script in the header script box which is given by font integrate service such as Google Web Fonts
Now integrate the font into your CSS Go to Appearance -> Customize/Theme Options -> Design Options Tab -> Custom CSS paste the following CSS code and Click on save button:
.widget-title {
font-family: "Philosopher",sans-serif;
}
Change above font family Philosopher with the one you have integrate as mentioned above.
Thank you!
.
.