3 black head stripes in smartphone

Hi
The logo, Menu and cart are defined in 3 different blocks, when u check them in mobile, you will see the logo and cart on first line and menu in the 2nd line
http://prntscr.com/i3qf94
There is not much space to fix all of them on one line.
You can check the site on real mobile devices, the width of the device lower than 368px will show the menu like in your screenshot because there is not enough width to fit them in one row.
If you want I can help you in css change to fit the logo and cart in one row for these devices too

Regards

Hi
Open /css/custom.css file in the template folder and add this code

@media (max-width: 360px) { .logo { width: auto; }}

save file, clear Joomla cache and check.

Regards

Hi
In the demo site, the menu is off-canvas menu, not the mega menu.
You can disable the collapse navigation for small screen from the template options.
And use the off-canvas sidebar to get the same view.
Here is documentation for menu system in this template.

Regards