How to change the width of the entire theme?

Hey there.  

So, I’ve read a lot of different questions and answers asking nearly the same question as my question.

Currently, what I have succeeded in changing, is making the sidebar width 300px, by adding this to the WP_head:

<style>
@media (min-width: 1110px) {
/* Main */
#main > .container > .row {
background-position: 760px 0;
} #primary {
width: 700px;
} .news-slider .carousel {
width: 480px;
} .news-slider .carousel-inner,
.news-slider .carousel .item,
.news-slider .carousel .carousel-inner .hentry {
height: 100%;
} .news-slider .carousel-list {
width: 219px;
} #secondary {
width: 300px;
} #secondary .entry-thumbnail img {
width: 300px;
} .single .site-content > .post .entry-content {
max-width: 530px;
}
}
</style>

 Now, when I do this, the main content area gets quite small because the width of the theme as a whole does not scale up when I change the sidebar width to 300px.  What I would like is for the entire theme to be a bit broader.

Could you please let me know how to do this? 

And thank you in advance for the answer! Your support is highly appreciated.