How to apply CSS in Lightning WebComponent

sampleStyling.html
==================
<template>
    <div align="center">
  <h1 class="FirstName">BrahmaNaidu</h1>
  <h1 class="LastName">Mandalapu</h1>
<div class="demo">
sfdcscenarios.blogspot.com
</div>
</div>
</template>
sampleStyling.css
=================
.FirstName
{
    color:red;
}
.LastName
{
    color:blue;
}
.demo
{
    color:yellowgreen;
}