:root {
    --primary-color: #0052CC;
    --primary-hover: #0747A6;
    --secondary-color: #42526E;
    --success-color: #00875A;
    --warning-color: #FF991F;
    --error-color: #DE350B;
    --background-color: #FAFBFC;
    --card-background: #FFFFFF;
    --border-color: #DFE1E6;
    --text-primary: #172B4D;
    --text-secondary: #6B778C;
    --shadow-light: 0 1px 2px rgba(0, 0, 0, 0.1);
    --shadow-medium: 0 2px 8px rgba(0, 0, 0, 0.12);
    --shadow-heavy: 0 8px 16px rgba(0, 0, 0, 0.15);
    --border-radius: 4px;
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-family);
    background-color: var(--background-color);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.app-container {
    flex: 1;
    display: flex;
    flex-direction: column;
}

/* Header */
.header {
    background-color: var(--card-background);
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow-light);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    color: var(--primary-color);
    font-size: 1.5rem;
    font-weight: 600;
}

.logo svg {
    width: 32px;
    height: 32px;
}

.language-selector select {
    padding: 0.5rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    background-color: var(--card-background);
    color: var(--text-primary);
    font-size: 0.875rem;
    cursor: pointer;
    transition: all 0.2s ease;
}

.language-selector select:hover {
    border-color: var(--primary-color);
}

/* Main Content */
.main-content {
    flex: 1;
    max-width: 1200px;
    width: 100%;
    margin: 2rem auto;
    padding: 0 2rem;
}

.calculator-container {
    display: grid;
    gap: 2rem;
}

/* Input Section */
.input-section {
    background-color: var(--card-background);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow-medium);
}

.input-section h2 {
    color: var(--text-primary);
    margin-bottom: 1.5rem;
    font-size: 1.25rem;
    font-weight: 600;
}

/* Tabs */
.tab-container {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 2rem;
    border-bottom: 2px solid var(--border-color);
}

.tab-button {
    padding: 0.75rem 1.5rem;
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    position: relative;
    transition: all 0.2s ease;
}

.tab-button:hover {
    color: var(--primary-color);
}

.tab-button.active {
    color: var(--primary-color);
}

.tab-button.active::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    right: 0;
    height: 2px;
    background-color: var(--primary-color);
}

.tab-content {
    display: none;
}

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

/* Form Elements */
.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
    font-weight: 500;
    font-size: 0.875rem;
}

.form-group input[type="text"],
.form-group input[type="number"],
.form-group select {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: 0.875rem;
    transition: all 0.2s ease;
    background-color: var(--card-background);
}

.form-group input:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 82, 204, 0.1);
}

.input-group {
    display: grid;
    grid-template-columns: 1fr auto;
    gap: 0.5rem;
}

.input-group select {
    width: auto;
    min-width: 200px;
}

/* Buttons */
.calculate-btn,
.tool-btn {
    padding: 0.75rem 1.5rem;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    display: inline-block;
}

.calculate-btn:hover,
.tool-btn:hover {
    background-color: var(--primary-hover);
    box-shadow: var(--shadow-light);
}

.calculate-btn {
    width: 100%;
    font-size: 1rem;
    padding: 1rem;
    margin-top: 0.5rem;
}

/* Results Section */
.results-section {
    background-color: var(--card-background);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow-medium);
    display: none;
}

.results-section h2 {
    color: var(--text-primary);
    margin-bottom: 1.5rem;
    font-size: 1.25rem;
    font-weight: 600;
}

.result-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
}

.result-item {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.result-item.full-width {
    grid-column: 1 / -1;
}

.result-item label {
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
}

.result-value {
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    font-family: 'Courier New', Courier, monospace;
    background-color: var(--background-color);
    padding: 0.5rem 0.75rem;
    border-radius: var(--border-radius);
    border: 1px solid var(--border-color);
}

/* Tools Section */
.tools-section {
    background-color: var(--card-background);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow-medium);
}

.tools-section h2 {
    color: var(--text-primary);
    margin-bottom: 1.5rem;
    font-size: 1.25rem;
    font-weight: 600;
}

.tool-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
}

.tool-card {
    background-color: var(--background-color);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    transition: all 0.2s ease;
}

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

.tool-card h3 {
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    font-size: 1.125rem;
    font-weight: 600;
}

.tool-card p {
    color: var(--text-secondary);
    font-size: 0.875rem;
    margin-bottom: 1rem;
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    overflow: auto;
}

.modal-content {
    background-color: var(--card-background);
    margin: 5% auto;
    padding: 2rem;
    border-radius: var(--border-radius);
    width: 90%;
    max-width: 800px;
    box-shadow: var(--shadow-heavy);
    position: relative;
}

.close {
    position: absolute;
    right: 1rem;
    top: 1rem;
    font-size: 2rem;
    font-weight: 300;
    color: var(--text-secondary);
    cursor: pointer;
    transition: color 0.2s ease;
}

.close:hover {
    color: var(--text-primary);
}

/* VLSM Specific */
.vlsm-requirement {
    display: grid;
    grid-template-columns: 1fr 200px auto;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
    align-items: center;
}

.vlsm-requirement input {
    padding: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
}

.remove-btn {
    background-color: var(--error-color);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    padding: 0.5rem 1rem;
    cursor: pointer;
    font-size: 1.125rem;
    transition: all 0.2s ease;
}

.remove-btn:hover {
    background-color: #C13E1B;
}

.vlsm-results-table {
    margin-top: 1.5rem;
}

.vlsm-result {
    background-color: var(--background-color);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 1rem;
    margin-bottom: 1rem;
}

.vlsm-result h4 {
    color: var(--primary-color);
    margin-bottom: 0.75rem;
}

.vlsm-result-details {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 0.5rem;
    font-size: 0.875rem;
}

.vlsm-result-details span {
    color: var(--text-secondary);
}

.vlsm-result-error {
    background-color: #FFEBE6;
    border: 1px solid #FFBDAD;
    border-radius: var(--border-radius);
    padding: 1rem;
    margin-bottom: 1rem;
    color: var(--error-color);
}

/* Split Results */
.split-results {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1rem;
    margin-top: 1rem;
}

.subnet-result {
    background-color: var(--background-color);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 1rem;
}

.subnet-result h4 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.subnet-result p {
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

/* Convert Results */
.convert-results {
    display: grid;
    gap: 1rem;
    margin-top: 1rem;
}

.convert-result {
    display: grid;
    grid-template-columns: 150px 1fr;
    gap: 1rem;
    align-items: center;
}

.convert-result label {
    color: var(--text-secondary);
    font-weight: 500;
}

.convert-result span {
    font-family: 'Courier New', Courier, monospace;
    background-color: var(--background-color);
    padding: 0.5rem 0.75rem;
    border-radius: var(--border-radius);
    border: 1px solid var(--border-color);
    word-break: break-all;
}

/* Footer */
.footer {
    background-color: var(--card-background);
    border-top: 1px solid var(--border-color);
    padding: 2rem;
    text-align: center;
    margin-top: auto;
}

.footer p {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* Responsive Design */
@media (max-width: 768px) {
    .header-content {
        padding: 1rem;
    }
    
    .main-content {
        padding: 0 1rem;
        margin: 1rem auto;
    }
    
    .input-section,
    .results-section,
    .tools-section {
        padding: 1.5rem;
    }
    
    .logo {
        font-size: 1.25rem;
    }
    
    .logo svg {
        width: 24px;
        height: 24px;
    }
    
    .input-group {
        grid-template-columns: 1fr;
    }
    
    .input-group select {
        width: 100%;
    }
    
    .result-grid {
        grid-template-columns: 1fr;
    }
    
    .tool-grid {
        grid-template-columns: 1fr;
    }
    
    .vlsm-requirement {
        grid-template-columns: 1fr;
    }
    
    .modal-content {
        width: 95%;
        margin: 2% auto;
        padding: 1.5rem;
    }
}

@media (max-width: 480px) {
    .tab-button {
        padding: 0.5rem 1rem;
        font-size: 0.75rem;
    }
    
    .calculate-btn {
        padding: 0.75rem;
    }
}

/* Dark Mode Support */
@media (prefers-color-scheme: dark) {
    :root {
        --background-color: #1F2937;
        --card-background: #111827;
        --border-color: #374151;
        --text-primary: #F9FAFB;
        --text-secondary: #D1D5DB;
        --primary-color: #3B82F6;
        --primary-hover: #2563EB;
    }
    
    .result-value,
    .convert-result span {
        background-color: #1F2937;
        border-color: #374151;
    }
    
    .tool-card {
        background-color: #1F2937;
    }
}