Once you define the Roboto font family, you have to apply it as the default font on the page:
body, .ui-btn {
font-family: Roboto-Light;
}
Make sure your path Fonts/Roboto-Light.ttf
is correct.
You can also use google fonts if you will be connected to the internet, put this line in your CSS:
@import url(http://fonts.googleapis.com/css?family=Roboto:400,300,500,700);
Also, for a more cross-browser solution you get eot, woff, and svg versions of the font as well as the ttf, then define the new font-face like this:
@font-face {
font-family: 'roboto';
src: url('fonts/roboto-regular-webfont.eot');
src: url('fonts/roboto-regular-webfont.eot?#iefix') format('embedded-opentype'),
url('fonts/roboto-regular-webfont.woff') format('woff'),
url('fonts/roboto-regular-webfont.ttf') format('truetype'),
url('fonts/roboto-regular-webfont.svg#robotoregular') format('svg');
font-weight: 400;
font-style: normal;
}
Here is a DEMO using google fonts