Headertop is not working well.

Hi, I have theme Minimal in WPLMS 3.9 and my headertop is not behaving like it should. When I visit the page start page it looks fine: https://brightauroras.com/wp-content/uploads/2021/04/Screenshot-2021-04-21-at-22.42.37.png And when I scroll its fixed and still looks great: https://brightauroras.com/wp-content/uploads/2021/04/Screenshot-2021-04-21-at-22.42.37.png Then the trouble starts. I go to my classed page and first visit it looks fine: https://brightauroras.com/wp-content/uploads/2021/04/Screenshot-2021-04-21-at-22.43.17.png But when I scroll its not fixed and the header is on top of it so can't buy a course as this is connected to create an account and login as well: https://brightauroras.com/wp-content/uploads/2021/04/Screenshot-2021-04-21-at-22.43.33.png So how can I keep the headertop fixed in the header so when I press Take Course I can add my details and follow instructions, now the login dropdown box end up right at the top of the page and on the mobile its impossible to see this. All this is applied to mobile so you know. Please see https://brightauroras.com and follow try to buy a course in your mobile. Thanks. Gabriella