Check out example codes for "how to use css". It will help you in understanding the concepts better.

Code Example 1

<link rel="stylesheet" href="file_name.css">

Code Example 2

<p style="color: blue; font-size: 46px;">

Code Example 3

<link rel="stylesheet" href="PathToYourFile.css">

Code Example 4

      height: 60%;
      margin-top: 7%;
      margin-left: 10%;
      margin-right: 10%;
      font-family: myriad-pro, sans-serif;
      font-style: normal;
      font-weight: 300;

Code Example 5

<link rel="stylesheet" type="text/css" href="mystyle.css">

Code Example 6

<link rel="stylesheet" href="stylesheet.css">
<div class="mydiv"></div>
.mydiv {
background-color: /*Color*/;
color: /*Another color*/;

Learn ReactJs, React Native from