/* =========================
   1. COLOR SYSTEM
========================= */

:root {
    /* Backgrounds */
    --background: #f5f7fa;
    --background-secondary: #eef2f7;
    --background-tertiary: #e5eaf1;
    --background-hover: #f1f5f9;
    --background-active: #e2e8f0;
    --background-overlay: #11182780;

    /* Cards */
    --card: #ffffff;
    --card-secondary: #f8fafc;
    --card-hover: #f9fafb;

    /* Text */
    --text: #111827;
    --secondary-text: #6b7280;
    --text-secondary: #6b7280;
    --text-tertiary: #9ca3af;
    --text-inverse: #ffffff;
    --text-disabled: #9ca3af;

    /* Borders */
    --border: #e5e7eb;
    --border-secondary: #d1d5db;
    --border-strong: #9ca3af;
    --border-focus: #2563eb;

    /* Primary */
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --primary-active: #1e40af;
    --primary-light: #dbeafe;

    /* Income */
    --income: #16a34a;
    --income-light: #dcfce7;
    --income-hover: #15803d;
    --income-text: #166534;

    /* Expenses */
    --expense: #dc2626;
    --expense-light: #fee2e2;
    --expense-hover: #b91c1c;
    --expense-text: #991b1b;

    /* Table */
    --table-header: #f3f4f6;
    --table-row: #ffffff;
    --table-row-alternate: #f8fafc;
    --table-row-hover: #f1f5f9;
    --table-border: #d1d5db;

    /* Inputs */
    --input-background: #ffffff;
    --input-background-hover: #f9fafb;
    --input-background-disabled: #f3f4f6;
    --input-border: #d1d5db;
    --input-border-focus: #2563eb;

    /* Status */
    --success: #15803d;
    --success-background: #dcfce7;
    --warning: #d97706;
    --warning-background: #fef3c7;
    --danger: #b91c1c;
    --danger-background: #fee2e2;
    --info: #2563eb;
    --info-background: #dbeafe;

    /* Effects */
    --muted: #9ca3af;
    --disabled-background: #f3f4f6;
    --shadow: #00000014;
    --shadow-strong: #00000026;
    --focus-ring: #93c5fd;

    /* Layout */
    --radius-sm: 6px;
    --radius-md: 12px;
    --radius-lg: 18px;
    --content-width: 1100px;
}


/* =========================
   2. GLOBAL STYLES
========================= */

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    padding: 40px 24px;
    background-color: var(--background);
    color: var(--text);
    font-family: Inter, -apple-system, BlinkMacSystemFont, "Segoe UI",
        Roboto, sans-serif;
    line-height: 1.5;
}

h1,
h2,
p {
    margin-top: 0;
}

h1,
h2 {
    letter-spacing: -0.03em;
}

button,
input,
select {
    font: inherit;
}


/* =========================
   3. HEADER
========================= */

header {
    max-width: var(--content-width);
    margin: 0 auto 36px;
    text-align: center;
}

header h1 {
    margin-bottom: 8px;
    color: var(--text);
    font-size: clamp(28px, 4vw, 38px);
    font-weight: 750;
}

header p {
    margin-bottom: 0;
    color: var(--secondary-text);
    font-size: 16px;
}


/* =========================
   4. FINANCIAL OVERVIEW
========================= */

.financial-overview {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 20px;
    width: 100%;
    max-width: var(--content-width);
    margin: 0 auto 32px;
}

.card {
    min-width: 0;
    padding: 24px;
    background-color: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    box-shadow: 0 4px 12px var(--shadow);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.card:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px var(--shadow);
}

.card h2 {
    margin-bottom: 12px;
    color: var(--secondary-text);
    font-size: 15px;
    font-weight: 600;
    letter-spacing: 0;
}

.card p {
    margin-bottom: 0;
    font-size: clamp(24px, 3vw, 32px);
    font-weight: 750;
    letter-spacing: -0.04em;
    overflow-wrap: anywhere;
}

.balance {
    color: var(--text);
}

.income {
    color: var(--income);
}

.expense {
    color: var(--expense);
}


/* =========================
   5. TRANSACTIONS SECTION
========================= */

.transactions {
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 24px;
    width: 100%;
    max-width: var(--content-width);
    margin: 0 auto;
}


/* =========================
   6. ADD TRANSACTION FORM
========================= */

.add-transaction {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 12px 16px;
    padding: 28px;
    background-color: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    box-shadow: 0 4px 12px var(--shadow);
}

.add-transaction-title {
    grid-column: 1 / -1;
    margin: 0 0 8px;
    color: var(--text);
    font-size: 20px;
    font-weight: 700;
    letter-spacing: -0.02em;
}

.add-transaction label {
    align-self: end;
    margin-top: 4px;
    color: var(--text);
    font-size: 14px;
    font-weight: 600;
}

.description,
.amount,
.type {
    width: 100%;
    min-width: 0;
    min-height: 46px;
    padding: 11px 13px;
    color: var(--text);
    background-color: var(--input-background);
    border: 1px solid var(--input-border);
    border-radius: var(--radius-sm);
    box-shadow: none;
    outline: none;
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.description:hover,
.amount:hover,
.type:hover {
    border-color: var(--border-strong);
}

.description:focus,
.amount:focus,
.type:focus {
    border-color: var(--input-border-focus);
    box-shadow: 0 0 0 3px var(--focus-ring);
}

.description::placeholder,
.amount::placeholder {
    color: var(--text-tertiary);
}

.type {
    cursor: pointer;
}

/* Native select option styling can vary by browser. */
.option-income {
    color: var(--income-text);
}

.option-expense {
    color: var(--expense-text);
}


/* =========================
   7. ADD TRANSACTION BUTTON
========================= */

#add-transaction-button {
    grid-column: 1 / -1;
    min-height: 48px;
    margin-top: 8px;
    padding: 12px 18px;
    color: var(--text-inverse);
    background-color: var(--primary);
    border: none;
    border-radius: var(--radius-sm);
    font-weight: 650;
    cursor: pointer;
    transition: background-color 0.2s ease, transform 0.2s ease;
}

#add-transaction-button:hover {
    background-color: var(--primary-hover);
}

#add-transaction-button:active {
    background-color: var(--primary-active);
    transform: scale(0.99);
}

#add-transaction-button:focus-visible {
    outline: 3px solid var(--focus-ring);
    outline-offset: 3px;
}


/* =========================
   8. TRANSACTION HISTORY
========================= */

.transaction-history {
    margin: 8px 0 -8px;
    color: var(--text);
    font-size: 22px;
    font-weight: 700;
}

.transaction-table {
    width: 100%;
    padding: 0;
    overflow: hidden;
    background-color: var(--table-row);
    border: 1px solid var(--border);
    border-collapse: separate;
    border-spacing: 0;
    border-radius: var(--radius-md);
    box-shadow: 0 4px 12px var(--shadow);
    text-align: left;
}

.transaction-table th,
.transaction-table td {
    padding: 15px 18px;
    border-right: 1px solid var(--table-border);
    border-bottom: 1px solid var(--table-border);
    vertical-align: middle;
}

.transaction-table th:last-child,
.transaction-table td:last-child {
    border-right: none;
}

.transaction-table tbody tr:last-child td {
    border-bottom: none;
}

.transaction-table th {
    color: var(--secondary-text);
    background-color: var(--table-header);
    font-size: 12px;
    font-weight: 700;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    white-space: nowrap;
}

.transaction-table td {
    color: var(--text);
    font-size: 14px;
}

.transaction-table tbody tr:nth-child(even) {
    background-color: var(--table-row-alternate);
}

.transaction-table tbody tr:hover {
    background-color: var(--table-row-hover);
}

/* Number and amount alignment */
.transaction-table th:first-child,
.transaction-table td:first-child {
    width: 64px;
    text-align: center;
}

.transaction-table th:nth-child(4),
.transaction-table td:nth-child(4) {
    text-align: right;
    white-space: nowrap;
}


/* =========================
   9. RESPONSIVE DESIGN
========================= */

@media (max-width: 760px) {
    body {
        padding: 28px 16px;
    }

    .financial-overview {
        grid-template-columns: 1fr;
        gap: 14px;
    }

    .card {
        padding: 20px;
    }

    .card p {
        font-size: 28px;
    }

    .add-transaction {
        padding: 22px;
    }

    /* Allow the table to scroll horizontally on small screens. */
    .transactions {
        min-width: 0;
    }

    .transaction-table {
        display: block;
        max-width: 100%;
        overflow-x: auto;
    }

    .transaction-table th,
    .transaction-table td {
        padding: 12px;
    }
}

@media (max-width: 440px) {
    body {
        padding: 24px 12px;
    }

    header {
        margin-bottom: 26px;
    }

    .add-transaction {
        grid-template-columns: 1fr;
        padding: 18px;
    }

    .add-transaction-title,
    #add-transaction-button {
        grid-column: auto;
    }

    .transaction-history {
        font-size: 20px;
    }
}

/* Respect users who prefer reduced motion. */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        scroll-behavior: auto !important;
        transition-duration: 0.01ms !important;
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
    }
}