:root {
    --primary-color: #111;
    --accent-color: #2563eb;
    --bg-color: #f9fafb;
    --card-bg: #ffffff;
    --text-main: #1f2937;
    --text-muted: #6b7280;
    --border-color: #e5e7eb;
    --danger-color: #ef4444;
    --success-color: #10b981;
    --radius-md: 12px;
    --radius-sm: 8px;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Inter', sans-serif;
}

body {
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.5;
    padding: 20px;
}

.app-container {
    max-width: 600px;
    margin: 0 auto;
    padding-bottom: 80px;
    /* Space for sticky button if needed */
}

header {
    text-align: center;
    margin-bottom: 32px;
}

header h1 {
    font-size: 1.5rem;
    font-weight: 700;
    letter-spacing: -0.025em;
}

.subtitle {
    color: var(--text-muted);
    font-size: 0.875rem;
}

/* Sections */
.card-section {
    margin-bottom: 32px;
}

.section-header {
    margin-bottom: 16px;
    display: flex;
    justify-content: space-between;
    align-items: baseline;
}

.section-header h2 {
    font-size: 1.125rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 8px;
}

.helper-text {
    font-size: 0.75rem;
    color: var(--text-muted);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 10px 16px;
    border-radius: var(--radius-md);
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
    border: none;
    font-size: 0.875rem;
    width: 100%;
}

.btn-outline {
    background: transparent;
    border: 1px dashed var(--border-color);
    color: var(--text-muted);
}

.btn-outline:hover {
    border-color: var(--text-main);
    color: var(--text-main);
    background: #fff;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    opacity: 0.9;
    transform: translateY(-1px);
}

.btn-lg {
    padding: 14px 20px;
    font-size: 1rem;
    margin-top: 24px;
}

.btn-icon {
    background: none;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    padding: 8px;
    border-radius: var(--radius-sm);
    transition: color 0.2s;
}

.btn-icon:hover {
    color: var(--danger-color);
    background-color: #fee2e2;
}

/* Inputs */
.input-group {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.input-group label {
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--text-muted);
}

input[type="text"],
input[type="number"] {
    padding: 10px 12px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
    width: 100%;
    outline: none;
    transition: border-color 0.2s;
}

input:focus {
    border-color: var(--accent-color);
    box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.1);
}

/* Gift Cards List */
.input-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
    margin-bottom: 16px;
}

.gift-card-row {
    display: grid;
    grid-template-columns: 2fr 1fr auto;
    gap: 12px;
    align-items: end;
    background: var(--card-bg);
    padding: 12px;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
}

/* Item Cards */
.items-grid {
    display: flex;
    flex-direction: column;
    gap: 16px;
    margin-bottom: 16px;
}

.item-card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 16px;
    box-shadow: var(--shadow-sm);
}

.item-row-top {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 12px;
    margin-bottom: 16px;
}

.item-name-group {
    flex: 1;
}

.item-row-bottom {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr;
    gap: 12px;
    align-items: end;
}

/* Stepper */
.stepper-group label {
    display: block;
    text-align: center;
    margin-bottom: 4px;
}

.stepper {
    display: flex;
    align-items: center;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    overflow: hidden;
    background: #fff;
}

.stepper-btn {
    background: #f3f4f6;
    border: none;
    width: 32px;
    height: 38px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    color: var(--text-main);
    font-size: 0.75rem;
}

.stepper-btn:active {
    background: #e5e7eb;
}

.stepper input {
    border: none;
    text-align: center;
    width: 100%;
    padding: 0;
    font-weight: 600;
    -moz-appearance: textfield;
}

.stepper input::-webkit-outer-spin-button,
.stepper input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

/* Results */
.hidden {
    display: none;
}

.summary-cards {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-bottom: 24px;
}

.summary-card {
    background: var(--card-bg);
    padding: 16px;
    border-radius: var(--radius-md);
    border: 2px solid transparent;
    /* Prepare for border change */
    border-color: var(--border-color);
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    box-shadow: var(--shadow-sm);
    cursor: pointer;
    transition: all 0.2s;
}

.summary-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.summary-card.selected {
    border-color: var(--accent-color);
    background-color: #eff6ff;
    /* Light blue tint */
}

/* Detailed Results */
.detailed-results {
    margin-top: 24px;
    padding-top: 24px;
    border-top: 1px solid var(--border-color);
    animation: fadeIn 0.3s ease-in-out;
}

.result-details {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
    margin-bottom: 24px;
}

.detail-column h4 {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
    margin-bottom: 12px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.detail-list {
    list-style: none;
    margin-bottom: 12px;
}

.detail-list li {
    font-size: 0.9rem;
    padding: 4px 0;
    border-bottom: 1px dashed var(--border-color);
}

.detail-list li:last-child {
    border-bottom: none;
}

.total-line {
    font-size: 0.9rem;
    margin-top: 8px;
    padding-top: 8px;
    border-top: 1px solid var(--border-color);
}

.final-summary {
    background: var(--bg-color);
    padding: 16px;
    border-radius: var(--radius-md);
    text-align: center;
    font-size: 1.1rem;
}

.empty-state {
    color: var(--text-muted);
    font-style: italic;
    font-size: 0.9rem;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@media (max-width: 500px) {
    .result-details {
        grid-template-columns: 1fr;
    }
}

.card-icon {
    font-size: 1.5rem;
    margin-bottom: 8px;
    color: var(--accent-color);
}

.summary-card h3 {
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 4px;
}

.summary-card .value {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-color);
}

.summary-card .desc {
    font-size: 0.7rem;
    color: var(--text-muted);
}

.best-topup .value {
    color: var(--success-color);
}

.best-loss .value {
    color: var(--danger-color);
}

@media (max-width: 400px) {
    .item-row-bottom {
        grid-template-columns: 1fr;
    }

    .stepper-group {
        width: 100%;
    }

    .stepper {
        justify-content: space-between;
    }

    .stepper input {
        width: 60px;
    }
}

/* Validation Styles */
.input-error {
    border-color: #ef4444 !important;
    /* Red-500 */
    animation: shake 0.5s cubic-bezier(.36, .07, .19, .97) both;
}

@keyframes shake {

    10%,
    90% {
        transform: translate3d(-1px, 0, 0);
    }

    20%,
    80% {
        transform: translate3d(2px, 0, 0);
    }

    30%,
    50%,
    70% {
        transform: translate3d(-4px, 0, 0);
    }

    40%,
    60% {
        transform: translate3d(4px, 0, 0);
    }
}

/* Footer */
.app-footer {
    text-align: center;
    margin-top: 40px;
    padding: 20px;
    color: var(--text-muted);
    font-size: 0.75rem;
}