Formatting tag

<p><strong>This is an important content</strong>, and this is normal content</p>  

<p> <i>Write Your Paragraph in italic text.</i></p>  

<p><em>This is an important content</em>, which displayed in italic font.</p>  

<h2>  I want to put a <mark> Mark</mark> on your face</h2>

<p> <u>Write Your Paragraph in underlined text.</u></p>  

<p> <strike>Write Your Paragraph with strikethrough</strike>.</p>

<p>Hello <big>Write the paragraph in larger font.</big></p>

<p>Hello <small>Write the paragraph in smaller font.</small></p>

X²+Y²<br>

H₂O