Welcome to the forums @carvhal. Your page looks good. Some things to revisit;
Verify your email addr with codepen so we can see your page full view
Codepen provides the boilerplate for you. It only expects the code you’d put within the body element in HTML. (No need to include the body tags). For anything you want to add to the <head> element click on the ‘Settings’ button, then HTML and add it into the ‘Stuff for <head>’ box.
Some people usually use grid for the entire page-layout and flex for formatting rows and columns.
CSS Grid for 2-axis layout, Flexbox for single axis (either X or Y) layout, as a general rule of thumb.