Stylesheet changes not working

[ Moderator note: title adjusted, please refrain from using help, urgent, emergency, asap, etc. in topic titles. ]

I’m messing around with the code in the style.css file but changes don’t seem to be occurring (like I think they would, or even at all) on my site when I update the file. I’m using Matheson theme, but there is zero activity over on their support forum.

I’ve been trying to change the font of both my site title and site description, along with inserting a break somewhere in the title. I also have been trying to make the space between my title and description larger, but any changes made to the .css file have not been changing anything. If I was able to use code in the WordPress theme customizing interface, I wouldn’t have these problems but life is not that easy.

Here is the code I suspect would need to be changed to accomplish what I’m trying to do, but nothing changes on the site when I update the file.

/* =Header
-------------------------------------------------------------- */
#header,
.header-meta {
  position: relative;
}

#site-meta {
  text-align: center;
  margin: 40px 0 60px;
}
@media (max-width: 768px) {
  #site-meta {
    margin-bottom: 0;
  }
}

#site-logo {
  margin: 30px 0 0 0;
}

.site-title {
  font-size: 60px;
  margin: 0;
}
.site-title a {
  text-decoration: none;
}

.site-description {
  margin: 0;
  font-size: 14px;
  line-height: 1;
}

.header-img {
  width: 100%;
  display: block;
}

#home-carousel .carousel-caption {
  bottom: auto;
  top: 10%;
}
@media (max-width: 480px) {
  #home-carousel .carousel-caption {
    display: none;
  }
}
#home-carousel h3,
#home-carousel p {
  color: #282828;
  text-shadow: none;
}
#home-carousel h3 {
  padding: 10px 60px;
  border: 2px solid #282828;
  display: inline-block;
  font-size: 40px;
}
#home-carousel p {
  font-size: 20px;
}
#home-carousel .item {
  max-height: 600px;
  overflow: hidden;
}
#home-carousel img {
  width: 100%;
}

Even modifying this part of the code

.site-title {
  font-size: 60px;
  margin: 0;
}

by changing font-size to 420px does nothing, which I find odd.

The whole Style.css containing ~8,200 lines of code for my Matheson themed site is here on pastebin if you want to take a look.

Any and all help would be greatly appreciated.