Interface vs implementation

<div class="visual contract" data-step="0"><div class="visual-head"><strong>ONE CONTRACT</strong><i></i></div><div class="visual-scene"><div class="contract-call">save()</div><div class="contract-wire">→</div><div class="contract-port">Storage<br><small>interface</small></div><div class="contract-wire">→</div><div class="contract-impl"><span>memory</span><span>file</span></div></div><div class="visual-caption"></div><div class="visual-dots"><b></b><b></b><b></b><b></b></div></div>

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.contract .visual-scene{display:flex;align-items:center;justify-content:center;gap:3px}.contract-call,.contract-port{border:1px solid var(--line);border-radius:7px;padding:9px 5px;background:var(--bg);text-align:center}.contract-call{font:600 12px ui-monospace,monospace}.contract-port{border-color:var(--accent)}.contract-port small{font-size:12px;color:var(--muted)}.contract-wire{color:var(--accent);font-size:18px}.contract-impl{display:flex;flex-direction:column;gap:5px}.contract-impl span{border:1px solid var(--line);border-radius:5px;background:var(--bg);padding:5px;transition:background .3s}.contract[data-step="0"] .contract-call,.contract[data-step="1"] .contract-port,.contract[data-step="2"] .contract-impl span:first-child,.contract[data-step="3"] .contract-impl span:last-child{background:color-mix(in srgb,var(--accent) 15%,var(--surface));border-color:var(--accent)}

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