app/views/layouts/icons/_envelope.html.slim
<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
<defs>
<style>.a{fill:none;stroke-linecap:round;stroke-linejoin:round;}</style>
</defs>
<rect class="a" x="0.5" y="4.5" width="23" height="15" rx="1.5" ry="1.5"></rect>
<polyline class="a" points="20.5 8.5 12 14 3.5 8.5"></polyline>
<line class="a" x1="3.5" y1="16" x2="7" y2="14"></line>
<line class="a" x1="20.5" y1="16" x2="17" y2="14"></line>
</svg>