.sci-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.5rem;
}
.sci-hint {
    margin-top: 0.5rem;
    color: #888;
    font-size: 0.95rem;
    text-align: center;
}

.finance-cards, .math-cards, .custom-cards {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    justify-content: center;
}
.finance-card, .math-card, .custom-card {
    background: #222;
    color: #fff;
    border-radius: 1rem;
    box-shadow: 0 2px 12px rgba(0,0,0,0.12);
    padding: 1rem;
    min-width: 220px;
    max-width: 260px;
    flex: 1 1 220px;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
}
.finance-card h4, .math-card h4, .custom-card h4 {
    margin: 0 0 0.5rem 0;
    font-size: 1.1rem;
    color: #ff9500;
}
.finance-card input, .math-card input, .custom-card input {
    width: 100%;
    margin-bottom: 0.3rem;
}
.finance-card .btn, .math-card .btn, .custom-card .btn {
    width: 100%;
    margin-bottom: 0.3rem;
}
.finance-card .calculator-display, .math-card .calculator-display, .custom-card .calculator-display {
    background: #111;
    color: #fff;
    font-size: 1.1rem;
    margin-bottom: 0;
}
.custom-card hr {
    width: 100%;
    border: 0;
    border-top: 1px solid #444;
    margin: 0.5rem 0;
}

@media (max-width: 900px) {
    .finance-cards, .math-cards, .custom-cards {
        flex-direction: column;
        align-items: stretch;
    }
}

body.dark .finance-card, body.dark .math-card, body.dark .custom-card {
    background: #181818;
    color: #fff;
    box-shadow: 0 2px 12px rgba(0,0,0,0.3);
}
body.dark .finance-card h4, body.dark .math-card h4, body.dark .custom-card h4 {
    color: #ffd700;
}
body {
    background: #f4f4f4;
    color: #222;
    margin: 0;
    font-family: 'Segoe UI', Arial, sans-serif;
    min-height: 100vh;
    transition: background 0.3s, color 0.3s;
}

header {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 1rem 0 0.5rem 0;
    background: #fff;
    box-shadow: 0 2px 8px rgba(0,0,0,0.04);
    position: sticky;
    top: 0;
    z-index: 10;
}

header h1 {
    margin: 0 0 0.5rem 0;
    font-size: 2rem;
}

nav {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
}

.nav-btn {
    background: #eee;
    border: none;
    border-radius: 0.5rem;
    padding: 0.5rem 1rem;
    font-size: 1rem;
    cursor: pointer;
    transition: background 0.2s;
}
.nav-btn.active, .nav-btn:hover {
    background: #007bff;
    color: #fff;
}

#darkModeToggle {
    background: #222;
    color: #fff;
    border: none;
    border-radius: 50%;
    width: 2.5rem;
    height: 2.5rem;
    font-size: 1.3rem;
    cursor: pointer;
    margin-top: 0.5rem;
    align-self: flex-end;
    transition: background 0.2s;
}
#darkModeToggle:hover {
    background: #444;
}

main {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    align-items: flex-start;
    gap: 2rem;
    padding: 2rem 1rem 1rem 1rem;
    max-width: 1200px;
    margin: 0 auto;
}

.calc-section {
    display: none;
    min-width: 320px;
    max-width: 400px;
    width: 100%;
}
.calc-section.active {
    display: block;
}

.calculator {
    background: #222;
    padding: 2rem 1rem;
    border-radius: 1rem;
    box-shadow: 0 4px 24px rgba(0,0,0,0.08);
    width: 100%;
    margin: 0 auto;
}

.calculator-display {
    width: 100%;
    height: 3rem;
    font-size: 2rem;
    margin-bottom: 1rem;
    border: none;
    border-radius: 0.5rem;
    padding: 0.5rem;
    background: #111;
    color: #fff;
    text-align: right;
}

.calculator-buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.5rem;
}

.btn {
    padding: 1rem;
    font-size: 1.2rem;
    border: none;
    border-radius: 0.5rem;
    background: #333;
    color: #fff;
    cursor: pointer;
    transition: background 0.2s;
}
.btn:hover {
    background: #444;
}
.operator {
    background: #ff9500;
    color: #fff;
}
#equals {
    grid-column: span 4;
    background: #28a745;
    color: #fff;
    font-size: 1.5rem;
}
#equals:hover {
    background: #218838;
}
#clear {
    background: #dc3545;
    color: #fff;
}
#clear:hover {
    background: #c82333;
}

#history {
    background: #fff;
    border-radius: 1rem;
    box-shadow: 0 2px 12px rgba(0,0,0,0.06);
    padding: 1rem;
    min-width: 220px;
    max-width: 300px;
    width: 100%;
    margin-top: 1rem;
    height: fit-content;
}
#history h3 {
    margin-top: 0;
}
#history-list {
    list-style: none;
    padding: 0;
    margin: 0;
    max-height: 300px;
    overflow-y: auto;
}
#history-list li {
    padding: 0.3rem 0.5rem;
    border-bottom: 1px solid #eee;
    font-size: 1rem;
}
#history-list li:last-child {
    border-bottom: none;
}

.result-tools {
    display: flex;
    gap: 1rem;
    margin: 1rem 0 0 0;
    justify-content: center;
}
.result-tools button {
    background: #007bff;
    color: #fff;
    border: none;
    border-radius: 0.5rem;
    padding: 0.5rem 1rem;
    font-size: 1rem;
    cursor: pointer;
    transition: background 0.2s;
}
.result-tools button:hover {
    background: #0056b3;
}

@media (max-width: 900px) {
    main {
        flex-direction: column;
        align-items: stretch;
        gap: 1rem;
    }
    .calc-section, #history {
        max-width: 100%;
        min-width: 0;
    }
}

@media (max-width: 600px) {
    header h1 {
        font-size: 1.2rem;
    }
    .calculator {
        padding: 1rem 0.5rem;
    }
    main {
        padding: 1rem 0.2rem;
    }
}

/* Dark mode */
body.dark {
    background: #181818;
    color: #f4f4f4;
}
body.dark header {
    background: #222;
    color: #fff;
    box-shadow: 0 2px 8px rgba(0,0,0,0.2);
}
body.dark .calculator {
    background: #181818;
    box-shadow: 0 4px 24px rgba(0,0,0,0.3);
}
body.dark .calculator-display {
    background: #222;
    color: #fff;
}
body.dark .btn {
    background: #333;
    color: #fff;
}
body.dark .btn:hover {
    background: #444;
}
body.dark .operator {
    background: #ff9500;
    color: #fff;
}
body.dark #equals {
    background: #28a745;
    color: #fff;
}
body.dark #equals:hover {
    background: #218838;
}
body.dark #clear {
    background: #dc3545;
    color: #fff;
}
body.dark #clear:hover {
    background: #c82333;
}
body.dark #history {
    background: #222;
    color: #fff;
    box-shadow: 0 2px 12px rgba(0,0,0,0.3);
}
body.dark .result-tools button {
    background: #007bff;
    color: #fff;
}
body.dark .result-tools button:hover {
    background: #0056b3;
}