Losing my sidebar inbetween set amount of PX

Hi there,

i have my left sidebar display a product filter so it is really important for my productpage. The sidebar went down as i minimized my screen and it got all the way to the bottom. With the help of you guys i got it to the top when i minimize my screen but now it completely disappears between 769 – 1079px. I have changed the “900px” part but that did not work. Any ideas what is happening here? If the site is needed ill make a codepen because the site is offline.

@media (max-width: 900px) {
	.site-content {
		display: -webkit-box;
		display: -moz-box;
		display: -ms-flexbox;
		display: -webkit-flex;
		display: flex;
		-webkit-flex-flow: row wrap;
		flex-flow: row wrap;
 	}

	#left-sidebar {
		-webkit-box-ordinal-group: 1;
		-moz-box-ordinal-group: 1;
		-ms-flex-order: 1;
		-webkit-order: 1;
		order: 1;
	}

	.content-area {
		-webkit-box-ordinal-group: 2;
		-moz-box-ordinal-group: 2;
		-ms-flex-order: 2;
		-webkit-order: 2;
		order: 2;
	}
}

Thanks for your time,

Sjoerd