Change font size – Design Swift

Hi team,

I tried to change the font size, but unfortunately it didn’t worked.

https://ampforwp.com/tutorials/article/how-to-change-font-style-in-amp/

For changing the header font size:
h1 .amp-wp-title {
font-family: Lato;
font-weight: bold;
font-size: 20px;
color: red;
}

For the text:
main .amp-wp-content {
font-size: 15px;
line-height: 29px;
color: #111;
}

Could you help here?

Best,
Ben