Change the entire website’s font-weight

My current version is Vantage PremiumVersion: 2.2.3. I would like to change the font-weight to 100. I tried changing it in the style.css file of the theme:

/*
Theme Name: Vantage Premium
Author: SiteOrigin
Author URI: http://siteorigin.com/
Theme URI: http://siteorigin.com/theme/vantage/
Description: Vantage is a flexible multipurpose theme. It's strength lies in its tight integration with some powerful plugins like Page Builder for responsive page layouts, MetaSlider for big beautiful sliders and WooCommerce to help you sell online. Vantage is fully responsive and retina ready. Use it to start a business site, portfolio or online store. We offer free and premium support on our support <a href="http://siteorigin.com/thread/">forums</a> (http://siteorigin.com/thread/).
Version: 2.2.3
License: GNU General Public License 2.0
License URI: license.txt
Tags: responsive-layout, fluid-layout, custom-background, custom-menu, featured-images, theme-options, threaded-comments, translation-ready, black, white, light, one-column, two-columns, full-width-template
*/
/* =Reset
-------------------------------------------------------------- */
html,
body,
div,
span,
applet,
object,
iframe,
h1,
h2,
h3,
h4,
h5,
h6,
p,
blockquote,
pre,
a,
abbr,
acronym,
address,
big,
cite,
code,
del,
dfn,
em,
font,
ins,
kbd,
q,
s,
samp,
small,
strike,
strong,
sub,
sup,
tt,
var,
dl,
dt,
dd,
ol,
ul,
li,
fieldset,
form,
label,
legend,
table,
caption,
tbody,
tfoot,
thead,
tr,
th,
td {
  border: 0;
  font-family: inherit;
  font-size: 100%;
  font-style: inherit;
  font-weight: inherit; 
  margin: 0;
  outline: 0;
  padding: 0;
  vertical-align: baseline;
}

Under the customization options, I can change almost everything, from font color to font size but not font-weight. How can I do so?

Best regards!!