Why some font-sizes rendered larger in mobile browsers?

My website's homepage have some h and div elements. The first h2 tag's and div tag's font sizes are with px. I have "-webkit-text-size-adjust: none;" spesification in html and body tags also. However the first tags's font size's rendered bigger in mobile browsers. Why? How can I solve this problem?

css codes:

h2 {
font-size: 16px;
}
#main h2 {
font-size: 16px;
font-weight: normal;
margin: 0;
}

.introdiv {
font-size: 12px;
line-height: 1.3;
margin: 0;
padding: 0 10px 24px 3px;
}