Twenty Thirteen theme post text size, how to make smaller

Did you try another browser / computer?

its not a computer or browser problem. i dont know which line i need to change to get smaller post title size
for example:
h2 {
font-size: 30px;
margin: 25px 0;
}
h3 {
font-size: 22px;
margin: 22px 0;
}
h4 {
font-size: 20px;
margin: 25px 0;
}

h5 {
font-size: 18px;
margin: 30px 0;
}

h6 {
font-size: 16px;
margin: 36px 0;
}
which one of this?

Are you using a child theme or a custom CSS plugin?

im using child theme

.entry-title {
font-size: 38px;
}

done with the title size.. h1 {
font-size: 28px;
but when i change size its also change color to the red.
..and one more question if its possible to remove that big Category Archives: blablabla.

If you forgot the closing curly bracket it could cause funny effects.

h1 {
font-size: 22px;
margin: 33px 0;
}