*{box-sizing:border-box;font-family:Arial,Helvetica,sans-serif}
body{margin:0;padding:0;background:#f7f7f7;color:#111}
.hero{background:#0a74da;color:#fff;padding:20px}
.container{display:flex;gap:16px;padding:16px}
.left,.center,.right{background:#fff;padding:12px;border-radius:6px;flex:1}
#invoice-preview{border:1px solid #ddd;padding:8px;min-height:200px}
.actions{margin-top:8px}
button{padding:8px 12px;margin:4px}
@media(max-width:800px){.container{flex-direction:column}}