*{margin:0;padding:0;box-sizing:border-box}
:root{
  --primary:#10b981;--primary-dark:#059669;--primary-light:#d1fae5;
  --danger:#ef4444;--danger-light:#fee2e2;
  --bg:#f9fafb;--surface:#ffffff;--surface-2:#f3f4f6;
  --border:#e5e7eb;--text:#111827;--text-2:#6b7280;--text-3:#9ca3af;
  --shadow:0 1px 3px rgba(0,0,0,.1);--shadow-md:0 4px 6px rgba(0,0,0,.07),0 1px 3px rgba(0,0,0,.06);
  --r:8px;--r-lg:12px;
}
body{font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',sans-serif;background:var(--bg);color:var(--text);line-height:1.5;min-height:100vh}

/* Auth */
.auth-page{display:flex;align-items:center;justify-content:center;min-height:100vh;padding:1rem}
.auth-card{background:var(--surface);border-radius:var(--r-lg);box-shadow:var(--shadow-md);padding:2rem;width:100%;max-width:400px}
.auth-logo{text-align:center;margin-bottom:1.5rem}
.auth-logo h1{font-size:2rem;font-weight:700;color:var(--primary)}
.auth-logo p{color:var(--text-2);font-size:.875rem;margin-top:4px}
.auth-footer{text-align:center;margin-top:1.25rem;font-size:.875rem;color:var(--text-2)}
.auth-footer a{color:var(--primary);text-decoration:none;font-weight:500}

/* Forms */
.form-group{margin-bottom:1rem}
.form-group label{display:block;font-size:.875rem;font-weight:500;margin-bottom:4px}
.form-group input,.form-group select{width:100%;padding:.625rem .75rem;border:1px solid var(--border);border-radius:var(--r);font-size:.9375rem;color:var(--text);background:var(--surface);outline:none;transition:border-color .15s}
.form-group input:focus,.form-group select:focus{border-color:var(--primary);box-shadow:0 0 0 3px rgba(16,185,129,.15)}

/* Buttons */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;padding:.625rem 1.25rem;border-radius:var(--r);font-size:.9375rem;font-weight:500;cursor:pointer;border:none;transition:all .15s;text-decoration:none}
.btn-primary{background:var(--primary);color:#fff;width:100%}
.btn-primary:hover{background:var(--primary-dark)}
.btn-secondary{background:var(--surface-2);color:var(--text);border:1px solid var(--border)}
.btn-secondary:hover{background:var(--border)}
.btn-danger{background:var(--danger);color:#fff;font-size:.8125rem;padding:4px 10px}
.btn-sm{padding:5px 14px;font-size:.8125rem}

/* Header */
.app-header{background:var(--surface);border-bottom:1px solid var(--border);padding:0 1.5rem;height:56px;display:flex;align-items:center;justify-content:space-between;position:sticky;top:0;z-index:10;box-shadow:var(--shadow)}
.app-header .logo{font-size:1.25rem;font-weight:700;color:var(--primary);text-decoration:none}
.app-header .user-info{display:flex;align-items:center;gap:1rem}
.app-header .user-name{font-size:.875rem;color:var(--text-2)}
.logout-btn{background:none;border:none;color:var(--text-2);font-size:.875rem;cursor:pointer;padding:4px 8px;border-radius:4px}
.logout-btn:hover{background:var(--surface-2);color:var(--text)}

/* Layout */
.container{max-width:920px;margin:0 auto;padding:1.5rem 1rem}
.page-header{display:flex;align-items:center;justify-content:space-between;margin-bottom:1.25rem}
.page-header h1{font-size:1.375rem;font-weight:700}
.back-link{display:inline-flex;align-items:center;gap:4px;color:var(--text-2);text-decoration:none;font-size:.875rem;margin-bottom:1rem}
.back-link:hover{color:var(--text)}
.section-grid{display:grid;grid-template-columns:1fr 1fr;gap:1rem;margin-bottom:1rem}
@media(max-width:640px){.section-grid{grid-template-columns:1fr}}

/* Cards */
.card{background:var(--surface);border-radius:var(--r-lg);box-shadow:var(--shadow);overflow:hidden;margin-bottom:1rem}
.card-header{padding:1rem 1.25rem;border-bottom:1px solid var(--border);display:flex;align-items:center;justify-content:space-between}
.card-header h2{font-size:1rem;font-weight:600}

/* Groups */
.group-item{display:flex;align-items:center;justify-content:space-between;padding:1rem 1.25rem;border-bottom:1px solid var(--border);text-decoration:none;color:inherit;transition:background .1s}
.group-item:last-child{border-bottom:none}
.group-item:hover{background:var(--bg)}
.group-name{font-weight:500;font-size:.9375rem}
.group-meta{font-size:.8125rem;color:var(--text-2);margin-top:2px}
.bal-pos{color:var(--primary);font-weight:600;font-size:.875rem}
.bal-neg{color:var(--danger);font-weight:600;font-size:.875rem}
.bal-zero{color:var(--text-3);font-size:.875rem}

/* Expenses */
.expense-item{padding:.875rem 1.25rem;border-bottom:1px solid var(--border);display:flex;align-items:center;justify-content:space-between}
.expense-item:last-child{border-bottom:none}
.expense-desc{font-weight:500;font-size:.9375rem}
.expense-meta{font-size:.8125rem;color:var(--text-2);margin-top:2px}
.expense-amount{font-size:1.125rem;font-weight:600}
.expense-delete{background:none;border:none;color:var(--text-3);cursor:pointer;font-size:1rem;padding:4px 8px;line-height:1}
.expense-delete:hover{color:var(--danger)}

/* Balances */
.balance-item{display:flex;align-items:center;justify-content:space-between;padding:.75rem 1.25rem;border-bottom:1px solid var(--border)}
.balance-item:last-child{border-bottom:none}
.balance-item .names{font-size:.9375rem}
.balance-item .amt{font-weight:600;color:var(--danger)}
.settle-btn{background:var(--primary);color:#fff;border:none;border-radius:4px;padding:4px 12px;font-size:.8125rem;cursor:pointer;font-weight:500}
.settle-btn:hover{background:var(--primary-dark)}

/* Members */
.member-item{display:flex;align-items:center;justify-content:space-between;padding:.625rem 1.25rem;border-bottom:1px solid var(--border)}
.member-item:last-child{border-bottom:none}
.avatar{width:32px;height:32px;border-radius:50%;background:var(--primary-light);color:var(--primary-dark);display:inline-flex;align-items:center;justify-content:center;font-weight:600;font-size:.875rem;margin-right:10px;flex-shrink:0}

/* Modal */
.modal-overlay{position:fixed;inset:0;background:rgba(0,0,0,.5);display:flex;align-items:center;justify-content:center;z-index:100;padding:1rem;opacity:0;pointer-events:none;transition:opacity .2s}
.modal-overlay.open{opacity:1;pointer-events:all}
.modal{background:var(--surface);border-radius:var(--r-lg);width:100%;max-width:480px;max-height:90vh;overflow-y:auto;transform:translateY(16px);transition:transform .2s}
.modal-overlay.open .modal{transform:translateY(0)}
.modal-header{padding:1.25rem;border-bottom:1px solid var(--border);display:flex;align-items:center;justify-content:space-between}
.modal-header h3{font-size:1.0625rem;font-weight:600}
.modal-close{background:none;border:none;font-size:1.25rem;cursor:pointer;color:var(--text-2);line-height:1}
.modal-body{padding:1.25rem}
.modal-footer{padding:1rem 1.25rem;border-top:1px solid var(--border);display:flex;gap:8px;justify-content:flex-end}

/* Split */
.split-toggle{display:flex;gap:8px;margin-bottom:1rem}
.split-type-btn{flex:1;padding:6px;border:1px solid var(--border);border-radius:var(--r);background:var(--surface-2);cursor:pointer;font-size:.875rem;font-weight:500}
.split-type-btn.active{background:var(--primary-light);border-color:var(--primary);color:var(--primary-dark)}
.split-row{display:flex;align-items:center;gap:8px;margin-bottom:8px}
.split-row label{flex:1;font-size:.9375rem;display:flex;align-items:center;gap:6px;cursor:pointer}
.split-row input[type=number]{width:90px;padding:4px 8px;border:1px solid var(--border);border-radius:var(--r)}
.split-row input[type=number]:focus{outline:none;border-color:var(--primary)}

/* Alerts */
.alert{padding:.75rem 1rem;border-radius:var(--r);font-size:.875rem;margin-bottom:1rem;display:none}
.alert.show{display:block}
.alert-error{background:var(--danger-light);color:#991b1b}
.alert-success{background:var(--primary-light);color:#065f46}

/* Utils */
.empty-state{text-align:center;padding:2.5rem 1rem;color:var(--text-2);font-size:.9375rem}
.spinner{display:inline-block;width:16px;height:16px;border:2px solid rgba(255,255,255,.4);border-top-color:#fff;border-radius:50%;animation:spin .6s linear infinite;vertical-align:middle}
@keyframes spin{to{transform:rotate(360deg)}}