Solved Change breakpoint & styling of mobile menu

Try the below:
1. Go to Theme Customizer -> Header & Navigation -> Header Format -> Header Style -> Choose 'Slide In' or 'Fullscreen'
2. Then paste the below CSS in Divi > Theme Options > Custom CSS:

Code:

@media screen and (max-width: 1320px) {
    .free-sticky {
        display: none!important;
    }
    #page-container #main-header, #page-container #top-header {
        display: block!important;
    }
    body #page-container {
        padding-top: 80px!important;
    }
}

**You may need to adjust some values to fit your need.

Seems to be your custom CSS issue. To fix it, try the below CSS in Divi > Theme Options > Custom CSS:

Code:

.et_pb_svg_logo #logo {
    height: 90%!important;
    max-width: 100%!important;
}
.et_header_style_left #page-container #et-top-navigation {
    padding-top: 24px!important;
}

**You may need to adjust some values to fit your need.