媒体查询css文件未检测到

I have designed a template and I wanted it to be responsive, so I included some media query files to achieve it. However the max-width: 500px file is not detecting properly. I really don't know how to solve it. The website works fine in all the other desktop screen resolutions. I don't know why it does not work in screen resolutions below 500px. All I did in that css file (medium-tab) was to turn the display to none for the menu-container and to activate the mobile container by writing display:block, so that the other menu will get activated automatically. How can I solve this issue? I have designed a template and I wanted it to b