font size css

.class {
	font-size: 12px;
}#selector{
    font-size:20px;
}p {
	font-size: 150% /*px, cm, in, etc.*/; 
}<span style="font-size:20px;"></span>// to scale font size in relation to its parent element
style="font-size: 2vw;"<body>      
         <h1 style="color:red;font-size:40px;">Heading</h1>      
         <p style="color:blue;font-size:18px;">This is demo text</p>    
      </body>