@epa-wg/custom-element/demo/demo.css

Declarative Custom Element as W3C proposal PoC with native(XSLT) based templating

html
{   font-family: -apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,Fira Sans,Droid Sans,Helvetica Neue,sans-serif;
    font-weight: 400; font-style: normal; -webkit-font-smoothing: antialiased;
}
body,nav{ display: flex; flex-wrap: wrap; align-content: stretch; gap: 1rem; }
body>*{flex: auto;}
nav
{   flex-direction: column;
    dce-root{ box-shadow:none; padding: 0;}
}

html-demo-element *:has(>dce-root){ box-shadow: 0 0 0.5rem lime; padding: 1rem;  flex:1; display: block; }
script{ display:none !important; }
dd{ padding: 1rem;}
p{ margin: 0;}
code{ font-weight: bold; color: green; text-wrap: nowrap; }

html-demo-element h3
{   text-shadow: 0 0 0.25em white;
    letter-spacing: 0.1rem;
}
*[slot="demo"]{ display: flex; gap: 1rem; flex-wrap: wrap; }