Show/hide elements at different screen sizes.
Uses SCSS breakpoint variables for consistent responsive behavior.
 Classes:

• .sm-hidden: Hidden on small screens (≤768px)
• .sm-only: Visible only on small screens (≤768px)
• .md-hidden: Hidden on medium screens (769px-1024px)
• .md-only: Visible only on medium screens (769px-1024px)
• .lg-hidden: Hidden on large screens (≥1024px)
• .lg-only: Visible only on large screens (≥1024px)

Examples

<!-- Show on mobile, hide on desktop -->
<div class="sm-only">Mobile content</div>
<!-- Hide on mobile, show on desktop -->
<div class="sm-hidden">Desktop content</div>
<!-- Show only on tablets -->
<div class="md-only">Tablet content</div>

Source: /Users/francisfontaine/Documents/GitHub/Standard/src/styles/standard-98-utilities.scss