styles.css

:root {
    --primary-color: #3498db;
    --operator-color: #f0ad4e;
    --equal-color: #5cb85c;
    --clear-color: #d9534f;
    --background-light: #f5f5f5;
    --text-light: #333;
    --button-light: #f0f0f0;
    --button-hover-light: #e0e0e0;
    --background-dark: #333;
    --text-dark: #f5f5f5;
    --button-dark: #444;
    --button-hover-dark: #555;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    transition: background-color 0.3s, color 0.3s;
}

/* Light theme */
body.light {
    background-color: var(--background-light);
    color: var(--text-light);
}

/* Dark theme */
body.dark {
    background-color: var(--background-dark);
    color: var(--text-dark);
}

body.dark .calculator,
body.dark .history-panel,
body.dark .unit-converter,
body.dark .currency-converter,
body.dark .age-calculator,
body.dark .formula-solver {
    background-color: var(--button-dark);
    color: var(--text-dark);
    border-color: #555;
}

body.dark button {
    background-color: var(--button-dark);
    color: var(--text-dark);
}

body.dark button:hover {
    background-color: var(--button-hover-dark);
}

body.dark input,
body.dark select {
    background-color: var(--button-dark);
    color: var(--text-dark);
    border-color: #666;
}

.app-container {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    padding: 20px;
}

.calculator-container {
    display: flex;
    gap: 20px;
    flex-grow: 1;
}

.theme-selector {
    margin-bottom: 20px;
    text-align: right;
}

.theme-selector button {
    padding: 8px 15px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
}

.theme-selector button:hover {
    opacity: 0.9;
}

/* Calculator Tabs */
.calculator-tabs {
    border: 1px solid #ccc;
    border-radius: 10px;
    overflow: hidden;
    flex-grow: 1;
}

.tabs-header {
    display: flex;
    background-color: #f0f0f0;
}

body.dark .tabs-header {
    background-color: #444;
}

.tab-btn {
    flex: 1;
    padding: 12px;
    border: none;
    background: none;
    cursor: pointer;
    font-size: 1em;
    border-bottom: 2px solid transparent;
    transition: all 0.2s;
}

.tab-btn:hover {
    background-color: #e0e0e0;
}

body.dark .tab-btn:hover {
    background-color: #555;
}

.tab-btn.active {
    border-bottom: 2px solid var(--primary-color);
    background-color: #e0e0e0;
    font-weight: bold;
}

body.dark .tab-btn.active {
    background-color: #555;
}

.tab-pane {
    display: none;
    padding: 15px;
}

.tab-pane.active {
    display: block;
}

/* Standard Calculator */
.standard-calculator,
.scientific-calculator {
    width: 100%;
    max-width: 300px;
    border: 1px solid #ccc;
    border-radius: 10px;
    padding: 15px;
    background-color: #f9f9f9;
    margin: 0 auto;
}

.display {
    margin-bottom: 15px;
    padding: 10px;
    background-color: #eee;
    border-radius: 5px;
    text-align: right;
    min-height: 60px;
}

body.dark .display {
    background-color: #555;
}

.previous-value {
    font-size: 0.9em;
    color: #666;
    min-height: 20px;
}

body.dark .previous-value {
    color: #aaa;
}

.current-value {
    font-size: 1.5em;
    font-weight: bold;
}

.buttons-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.scientific-calculator .buttons-grid {
    grid-template-columns: repeat(5, 1fr);
}

.span-2 {
    grid-column: span 2;
}

button {
    padding: 12px;
    border: none;
    border-radius: 6px;
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    background-color: var(--button-light);
    color: var(--text-light);
}

button:hover {
    background-color: var(--button-hover-light);
    transform: translateY(-1px);
}

button:active {
    transform: translateY(0);
}

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

.operator:hover {
    background-color: #ec971f;
}

/* Converter Styles */
.unit-converter,
.currency-converter,
.age-calculator,
.formula-solver {
    width: 100%;
    max-width: 500px;
    border: 1px solid #ccc;
    border-radius: 10px;
    padding: 15px;
    background-color: #f9f9f9;
    margin: 0 auto;
}

h3 {
    margin-top: 0;
    margin-bottom: 15px;
}

.converter-controls,
.calculator-controls,
.formula-controls {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

input, select {
    padding: 8px;
    border-radius: 4px;
    border: 1px solid #ccc;
}

button.convert-btn {
    padding: 10px;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
}

button.convert-btn:hover {
    background-color: #2980b9;
}

.conversion-result,
.age-result {
    margin-top: 15px;
    padding: 10px;
    background-color: #e8f4f8;
    border-radius: 4px;
    font-weight: bold;
}

body.dark .conversion-result,
body.dark .age-result {
    background-color: #2c3e50;
}

/* Formula Solver */
.formula-description {
    font-style: italic;
    color: #666;
    margin-bottom: 10px;
}

body.dark .formula-description {
    color: #aaa;
}

.variables-input {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.variable-input {
    display: flex;
    align-items: center;
}

.variable-input label {
    width: 80px;
}

.variable-input input {
    flex-grow: 1;
}

.solution {
    margin-top: 15px;
    padding: 10px;
    background-color: #e8f8e8;
    border-radius: 4px;
}

body.dark .solution {
    background-color: #2c3e50;
}

.solution h4 {
    margin-bottom: 5px;
}

.result {
    font-weight: bold;
    margin-bottom: 10px;
}

.solution-steps {
    margin-top: 5px;
    padding-left: 20px;
}

.solution-steps li {
    margin-bottom: 5px;
}

/* History Panel */
.history-panel {
    width: 300px;
    border: 1px solid #ccc;
    border-radius: 10px;
    padding: 15px;
    background-color: #f9f9f9;
    display: flex;
    flex-direction: column;
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
}

.history-header h3 {
    margin: 0;
}

.history-header button {
    padding: 5px 10px;
    background-color: var(--clear-color);
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
}

.history-header button:hover {
    background-color: #c9302c;
}

.history-list {
    list-style: none;
    padding: 0;
    margin: 0;
    flex-grow: 1;
    overflow-y: auto;
    max-height: 500px;
}

.history-item {
    padding: 8px;
    margin-bottom: 5px;
    background-color: #eee;
    border-radius: 4px;
    cursor: pointer;
    word-break: break-all;
}

body.dark .history-item {
    background-color: #555;
}

.history-item:hover {
    background-color: #ddd;
}

body.dark .history-item:hover {
    background-color: #666;
}

.empty-history {
    padding: 8px;
    color: #666;
    font-style: italic;
    text-align: center;
}

/* Responsive Design */
@media (max-width: 768px) {
    .calculator-container {
        flex-direction: column;
    }
    
    .history-panel {
        width: 100%;
        margin-top: 20px;
    }
    
    .tabs-header {
        flex-wrap: wrap;
    }
    
    .tab-btn {
        padding: 8px;
        font-size: 0.9em;
    }
}