Look up some css frameworks.
Take a look at ohter sites, perhaps on some showcases or portfolios of professional artist or semi professional, established, indi devs.
Don't use this kind of background graphics.
I am a friend of "no background graphics at all".
Read up css manuals and center your webpage.
Use some nice fixed width. I don't know which width is "in" these days.
Choose one stylish color scheme. Not too many colors.

I hate it when showcases or shopsites expand to the total display width. Cap the size or rearange the formation of your gamedownloads.

And use another header graphic. It seems ... stretched(?), and low res (that for sure).

I can't show you any example of an ideal website, because that depends on taste. But your website is way too oldschool. I know you showcase your games for free there. But imagine you want to get work somewhere as a dev and they see a website like this. I think nobody will be impressed by this.