To set font size with pixels, use the em unit, with the font-size property.
1em = 16px
Example
You can try to run the following code to set font size with em
<!DOCTYPE html> <html> <head> <style> h1 { /* 30px/16 = 1.875em */ font-size: 1.875em; } </style> </head> <body> <h1>This is demo heading</h1> <p>This is demo text.</p> </body> </html>