:root {
    --primary-color: #2196f3;
    --primary-light: #64b5f6;
    --primary-dark: #1976d2;
    --secondary-color: #f50057;
    --background-color: #f8fafc;
    --surface-color: #ffffff;
    --text-primary: #1a2027;
    --text-secondary: #64748b;
    --border-radius: 12px;
    --spacing-unit: 8px;
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --gradient-primary: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    transition: all 0.3s ease;
}

body {
    font-family: 'Roboto', sans-serif;
    background-color: var(--background-color);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

#app {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.header {
    background: var(--gradient-primary);
    color: white;
    padding: calc(var(--spacing-unit) * 4) calc(var(--spacing-unit) * 3);
    text-align: center;
    box-shadow: var(--shadow-md);
    position: relative;
    overflow: hidden;
}

.header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: radial-gradient(circle at center, rgba(255,255,255,0.1) 0%, rgba(255,255,255,0) 70%);
    pointer-events: none;
}

.header h1 {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-unit);
    font-weight: 700;
    letter-spacing: -0.5px;
}

.header p {
    font-size: 1.1rem;
    opacity: 0.9;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: calc(var(--spacing-unit) * 4);
    flex-grow: 1;
}

.conversion-section {
    background-color: var(--surface-color);
    border-radius: var(--border-radius);
    padding: calc(var(--spacing-unit) * 4);
    box-shadow: var(--shadow-lg);
    border: 1px solid rgba(0, 0, 0, 0.05);
}

.conversion-section h2 {
    text-align: center;
    margin-bottom: calc(var(--spacing-unit) * 4);
    color: var(--text-primary);
    font-weight: 500;
    font-size: 1.5rem;
}

.conversion-types {
    display: flex;
    justify-content: center;
    gap: calc(var(--spacing-unit) * 1.5);
    margin-bottom: calc(var(--spacing-unit) * 4);
    flex-wrap: wrap;
    padding: 0 calc(var(--spacing-unit) * 2);
}

.conversion-type {
    padding: calc(var(--spacing-unit) * 1.5) calc(var(--spacing-unit) * 3);
    border: none;
    border-radius: var(--border-radius);
    background-color: var(--background-color);
    color: var(--text-primary);
    cursor: pointer;
    transition: all 0.3s ease;
    font-size: 1rem;
    font-weight: 500;
    box-shadow: var(--shadow-sm);
    position: relative;
    overflow: hidden;
}

.conversion-type:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
    background-color: var(--primary-light);
    color: white;
}

.conversion-type.active {
    background: var(--gradient-primary);
    color: white;
    box-shadow: var(--shadow-md);
}

.conversion-type:active {
    transform: translateY(1px);
}

.converter {
    display: none;
    flex-direction: column;
    gap: calc(var(--spacing-unit) * 3);
    max-width: 600px;
    margin: 0 auto;
    opacity: 0;
    transform: translateY(10px);
    transition: all 0.3s ease;
}

.converter.active {
    display: flex;
    opacity: 1;
    transform: translateY(0);
}

.input-group {
    display: flex;
    gap: var(--spacing-unit);
    background: white;
    padding: calc(var(--spacing-unit) * 1.5);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(0, 0, 0, 0.05);
}

.input-group:focus-within {
    box-shadow: var(--shadow-md);
    border-color: var(--primary-light);
}

.input-group input,
.input-group select {
    padding: calc(var(--spacing-unit) * 1.5);
    border: 1px solid #e2e8f0;
    border-radius: var(--border-radius);
    font-size: 1rem;
    background-color: white;
    color: var(--text-primary);
    transition: all 0.3s ease;
}

.input-group input:focus,
.input-group select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.input-group input {
    flex: 2;
}

.input-group select {
    flex: 1;
    cursor: pointer;
}

.swap-button {
    align-self: center;
    background: none;
    border: none;
    color: var(--primary-color);
    cursor: pointer;
    padding: var(--spacing-unit);
    border-radius: 50%;
    transition: all 0.3s ease;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.swap-button:hover {
    background-color: rgba(33, 150, 243, 0.1);
    transform: scale(1.1);
}

.swap-button:active {
    transform: scale(0.95);
}

.molecular-weight-input,
.dna-params,
.pcr-params,
.percentage-calculator {
    margin-top: calc(var(--spacing-unit) * 3);
    padding: calc(var(--spacing-unit) * 3);
    background-color: #f8fafc;
    border-radius: var(--border-radius);
    border: 1px solid rgba(0, 0, 0, 0.05);
    box-shadow: var(--shadow-sm);
}

.molecular-weight-input label,
.param-group label {
    display: block;
    margin-bottom: var(--spacing-unit);
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
}

.molecular-weight-input input,
.param-group input,
.param-group select,
.common-mw-selector select {
    width: 100%;
    padding: calc(var(--spacing-unit) * 1.5);
    border: 1px solid #e2e8f0;
    border-radius: var(--border-radius);
    font-size: 1rem;
    background-color: white;
    transition: all 0.3s ease;
}

.molecular-weight-input input:focus,
.param-group input:focus,
.param-group select:focus,
.common-mw-selector select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.common-mw-selector {
    margin-top: calc(var(--spacing-unit) * 2);
}

.percentage-type-selector {
    display: flex;
    gap: calc(var(--spacing-unit) * 2);
    margin-bottom: calc(var(--spacing-unit) * 3);
    flex-wrap: nowrap;
    justify-content: space-between;
    width: 100%;
    padding: 0 calc(var(--spacing-unit) * 2);
}

.percentage-type-selector input[type="radio"] {
    display: none;
}

.percentage-type-selector label {
    padding: calc(var(--spacing-unit) * 1.5) calc(var(--spacing-unit) * 2);
    border-radius: var(--border-radius);
    background-color: white;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    gap: var(--spacing-unit);
    box-shadow: var(--shadow-sm);
    white-space: nowrap;
    flex: 1;
    justify-content: center;
    font-size: 0.9rem;
    max-width: 32%;
    min-width: 140px;
}

.percentage-type-selector .material-icons-round {
    font-size: 1.2rem;
}

.percentage-type-selector label:hover {
    background-color: var(--primary-light);
    color: white;
}

.percentage-type-selector input[type="radio"]:checked + label {
    background: var(--gradient-primary);
    color: white;
}

.calculation-result {
    margin-top: calc(var(--spacing-unit) * 2);
    padding: calc(var(--spacing-unit) * 2);
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-sm);
}

.calculation-result div {
    padding: calc(var(--spacing-unit));
    color: var(--text-primary);
    font-weight: 500;
}

.calculation-explanation {
    margin-top: calc(var(--spacing-unit) * 2);
    padding: calc(var(--spacing-unit) * 2);
    background-color: #f8fafc;
    border-radius: var(--border-radius);
    border: 1px solid rgba(0, 0, 0, 0.05);
    box-shadow: var(--shadow-sm);
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.calculation-explanation:empty {
    display: none;
}

.calculation-explanation strong {
    color: var(--text-primary);
    font-weight: 500;
}

.footer {
    background-color: var(--surface-color);
    padding: calc(var(--spacing-unit) * 3);
    text-align: center;
    color: var(--text-secondary);
    margin-top: auto;
    box-shadow: var(--shadow-md);
    border-top: 1px solid rgba(0, 0, 0, 0.05);
}

/* Responsive Design */
@media (max-width: 768px) {
    .header h1 {
        font-size: 2rem;
    }

    .container {
        padding: var(--spacing-unit);
    }

    .conversion-section {
        padding: calc(var(--spacing-unit) * 2);
    }

    .input-group {
        flex-direction: column;
    }

    .input-group input,
    .input-group select {
        width: 100%;
    }

    .conversion-types {
        gap: calc(var(--spacing-unit));
    }

    .conversion-type {
        flex: 1 1 calc(50% - var(--spacing-unit));
        min-width: 150px;
        text-align: center;
    }

    .percentage-type-selector {
        flex-wrap: wrap;
        gap: calc(var(--spacing-unit));
        padding: 0;
    }

    .percentage-type-selector label {
        flex: 1 1 auto;
        min-width: 140px;
        max-width: none;
        font-size: 0.85rem;
        padding: calc(var(--spacing-unit) * 1.2) calc(var(--spacing-unit) * 1.5);
    }
}

@media (max-width: 480px) {
    .header h1 {
        font-size: 1.5rem;
    }

    .conversion-type {
        width: 100%;
    }

    .molecular-weight-input,
    .dna-params,
    .pcr-params,
    .percentage-calculator {
        padding: calc(var(--spacing-unit) * 2);
    }
}