My Website Scrambles Out Of Order When I Minimize The Browser

When I minimize my browser window the navigation menu and pretty much my whole website scrambles out of order. I want my menu bar and entire website to maintain its positioning when I minimize the browser window. I assume I need to add a container or wrapper around the menu and around the entire website in order to hold them in position so that nothing moves out of place when I minimize the browser window. Everything looks fine as long as the browser window is maximized. Even when I minimize the browser window everything looks fine, but if I minimize the browser window to where the width of the window is smaller than the width of the menu bar then the whole website scrambles out of order. Please help me fix this issue. My website is https://www.retroworldtoys.com.