To select all elements with class=”mydemo”, you can try to run the following code. Use the .class CSS selector to achieve this,
Example
<!DOCTYPE html> <html> <head> <style> .demo { border: 2px dashed orange; } </style> </head> <body> <h1 class = "demo">Heading 1</h1> <h1>Heading 1</h1> <h2>Heading 2</h2> </body> </html>