Two columns at smallest screen size

Hello,
I need help tweaking the CSS please.

The code below works to display columns at 50% width, but I haven’t found a setting to make image height proportional. Thumbs are still displayed as if the columns were 100% wide.

@media all and (max-width:480px) {
 #sb_instagram.sbi_col_10 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_3 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_4 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_5 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_6 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_7 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_8 #sbi_images .sbi_item,
 #sb_instagram.sbi_col_9 #sbi_images .sbi_item {
  width:50% !important;
 }

}