I gave unique IDs to SVG path elements - opacity-1n and opacity-1e. My aim is to make opacity-1e visible when hovering over opacity-1n.
<g id="Layer_1">
<path id="opacity-1n" d="M135.4 6.8v38.3h-1.9l-15.1-13.8-1.8-1.6-6.8-6.2-2-1.8v23.4h-7.7V6.7h1.9L119.1 22l1.9 1.7 6.7 5.9V6.8z" class="st0"/>
<path id="opacity-1e" d="M196.9 22.9h18.2v6.3h-18.2v9.1H219v6.8h-29.8V6.7H219v6.8h-22.1z" class="st0"/>
</g>
#opacity-1n:hover #opacity-1e {opacity: 1;}
#opacity-1e {opacity: 0;}
Other attempts:
#opacity-1n:hover + #opacity-1e {opacity: 1;}
#opacity-1n:hover > #opacity-1e {opacity: 1;}
#opacity-1n:hover ~ #opacity-1e {opacity: 1;}