Style.css file versus styles.css file?

I want to make a slight change in a theme that I’m using. The theme’s author said to insert a string at the bottom of the styles.css file.

But I can’t find a styles.css file for this theme, only a style.css file. And that has only 26 lines, most of which is meta-data about the theme: name, author, version #, License, etc.

The rest of the content is:

@import url(“css/reset.css”);
@import url(“css/animate.css”);
@import url(“css/mediaelementplayer.css”);
@import url(“font/font-awesome.min.css”);
@import url(“css/skeleton.css”);
@import url(“css/layout.css”);

None of which seems to relate to the code he is saying I should put in:

.price-table.highlighted { background: #yourColor !important }

section.samples { background: #yourColor !important }

#cta-bar { background: #yourColor !important }

I don’t want to ask him about this if I just can’t find where to put this due to my inexperience.

I’ve looked in all the folders for this theme and can’t find a styles.css file.

What am I misunderstanding?