Mobile version not working

Hi,

Not sure what has happened, but the mobile version of my site studiowindmill.com.au stopped looking like the theme entirely.

I have added some custom CSS to change the colour scheme and centre galleries:

button,
.main-navigation {
	background-color: #60c6cc;
}

.nav-menu > li > a:after {
	color: #ffffff;
}
button,
.main-navigation {
	background-color: #60c6cc;
}

.main-navigation .nav-menu > li > a:after,
	.main-navigation .menu > li > a:after {
	color: #FFFFFF;
	content: \\\\\2022;
	margin-left: 1em;
	color: #ffffff;
}
.social-links ul a:before {
	background: #60c6cc;
}

input[type="submit"] {
	background-color: #60c6cc;
}

.site-info {
	visibility: hidden;
}

/* 
The below is to centre galleries

https://ww.wp.xz.cn/support/topic/gallery-alignment-2/
.gallery {
	display: flex;
	justify-content: center;
	flex-wrap: wrap;
	margin: 0 auto;
}

.gallery-columns-3 {
	display: flex;
	justify-content: center;
	width: 66%;
	margin: 0 auto;
}

.gallery-columns-4 {
	display: flex;
	justify-content: center;
	width: 80%;
	margin: 0 auto;
}

.gallery-columns-5 {
	display: flex;
	justify-content: center;
	width: 100%;
	margin: 0 auto;
}

I am using a child theme setup too.

Hope someone can help,
Dave