:root {
    --bg-color: #f4f4f4;
    --container-bg: #fff;
    --section-bg: #f9f9f9;
    --text-color: #333;
    --border-color: #ddd;
    --modal-bg: #fefefe;
    --modal-shadow: rgba(0,0,0,0.4);
    --button-primary-bg: #007bff;
    --button-danger-bg: #dc3545;
    --button-success-bg: #28a745;
    --button-warning-bg: #f0ad4e;
    --button-secondary-bg: #6c757d;
    --header-text-color: #333;
    --amount-text-color: #d9534f;
}

body.dark-mode {
    --bg-color: #121212;
    --container-bg: #1e1e1e;
    --section-bg: #2c2c2c;
    --text-color: #e0e0e0;
    --border-color: #444;
    --modal-bg: #333;
    --modal-shadow: rgba(0,0,0,0.7);
    --button-primary-bg: #0d6efd;
    --header-text-color: #e0e0e0;
}

body {
    font-family: sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    margin: 0;
    padding: 20px 0;
    transition: background-color 0.3s, color 0.3s;
}
.container {
    max-width: 800px;
    margin: auto;
    background: var(--container-bg);
    padding: 20px;
    border-radius: 12px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}
.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 10px;
    margin-bottom: 20px;
}
h1 {
    text-align: left;
    margin: 0;
    font-size: 1.8em;
}
h1, h2 {
    color: var(--header-text-color);
}
h2 {
    text-align: center;
}
.section {
    background: var(--section-bg);
    border: 1px solid var(--border-color);
    padding: 20px;
    margin-bottom: 20px;
    border-radius: 8px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.05);
}
button {
    background-color: var(--button-primary-bg);
    color: white;
    padding: 10px 15px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1em;
    transition: opacity 0.2s;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
}
button:hover {
    opacity: 0.9;
}
#theme-toggle-btn {
    background-color: var(--button-secondary-bg);
}
#calculate-btn {
    width: 100%;
    padding: 15px;
    font-size: 1.2em;
    background-color: var(--button-success-bg);
}
#reset-btn {
    background-color: var(--button-danger-bg);
}
#toggle-decimal-btn {
    background-color: var(--button-warning-bg);
}
input[type="text"], input[type="number"], select {
    width: 100%;
    padding: 8px;
    border: 1px solid var(--border-color);
    background-color: var(--container-bg);
    color: var(--text-color);
    border-radius: 4px;
    box-sizing: border-box;
}
.button-group {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-top: 15px;
}
.member-checkbox-item {
    display: flex;
    align-items: center;
}
.expense-item {
    border: 1px solid var(--border-color);
    padding: 15px;
    margin-bottom: 15px;
    border-radius: 5px;
    background: var(--container-bg);
}
.expense-item .delete-item-btn, .delete-member-btn {
    background-color: var(--button-danger-bg);
}
.payer-list-item {
    border: 1px dashed var(--border-color);
    display: flex;
    gap: 10px;
    align-items: center;
    margin-bottom: 5px;
    padding: 5px;
    border-radius: 4px;
}
.payer-list-item > div:first-child { flex: 2; }
.payer-list-item > div:nth-child(2) { flex: 1; }
.payer-list-item .delete-payer-btn {
    background-color: var(--button-secondary-bg);
    padding: 5px 8px;
    font-size: 0.8em;
}
#payment-instructions ul {
    list-style: none;
    padding: 0;
}
#payment-instructions li {
    padding-left: 2.5em;
    position: relative;
    margin-bottom: 8px;
}
/* #payment-instructions li::before {
    content: '💸';
    position: absolute;
    left: 0;
    top: 0;
    font-size: 1.2em;
} */
.modal {
    display: none;
    position: fixed;
    z-index: 1;
    left: 0; top: 0;
    width: 100%; height: 100%;
    overflow: auto;
    background-color: var(--modal-shadow);
}
.modal-content {
    background-color: var(--modal-bg);
    margin: 15% auto;
    padding: 20px;
    border: 1px solid #888;
    width: 80%;
    max-width: 500px;
    border-radius: 8px;
}
.close-btn {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
    cursor: pointer;
}
#managed-member-list li {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 8px;
    border-bottom: 1px solid var(--border-color);
}
#total-amount, #average-amount {
    font-weight: bold;
    color: var(--amount-text-color);
    font-size: 1.1em;
}
#individual-payments-container, #individual-debts-container {
    margin-bottom: 15px;
}
#individual-payments-container ul, #individual-debts-container ul {
    list-style: none;
    padding: 0; margin: 0;
}
#individual-payments-container li, #individual-debts-container li {
    display: flex;
    justify-content: space-between;
    padding: 8px 5px;
    border-bottom: 1px solid var(--border-color);
}
#individual-payments-container li:last-child, #individual-debts-container li:last-child {
    border-bottom: none;
}
#toggle-payments-btn, #toggle-debts-btn {
    background-color: var(--button-secondary-bg);
    flex-grow: 1;
    flex-basis: 0;
}
#toast-container {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 1000;
    display: flex;
    flex-direction: column;
    gap: 10px;
}
.toast {
    padding: 15px 20px;
    color: white;
    border-radius: 8px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.2);
    opacity: 1;
    transition: opacity 0.5s, transform 0.5s;
    transform: translateX(0);
}
.toast.fade-out {
    opacity: 0;
    transform: translateX(100%);
}
.toast.success { background-color: #28a745; }
.toast.error { background-color: #dc3545; }

@media (max-width: 768px) {
    body {
        margin: 0;
        padding-top: 10px;
    }
    .container {
        width: 100%;
        padding: 15px;
        border-radius: 0;
        box-shadow: none;
    }
    h1 { font-size: 1.5em; }
}