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

:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-color: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-hover: 0 4px 6px rgba(0, 0, 0, 0.1);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background: var(--card-bg);
    padding: 40px 0;
    text-align: center;
    border-bottom: 1px solid var(--border-color);
}

header h1 {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 10px;
}

header .subtitle {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

.tool-nav {
    background: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav-list {
    display: flex;
    list-style: none;
    gap: 5px;
    overflow-x: auto;
    padding: 10px 0;
}

.nav-list li {
    flex-shrink: 0;
}

.nav-link {
    display: block;
    padding: 10px 20px;
    text-decoration: none;
    color: var(--text-secondary);
    border-radius: 6px;
    transition: all 0.2s;
    white-space: nowrap;
}

.nav-link:hover,
.nav-link.active {
    background: var(--primary-color);
    color: white;
}

main {
    padding: 40px 20px;
    min-height: calc(100vh - 200px);
}

.page {
    display: none;
}

.page.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.tool-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: 20px;
}

.tool-card {
    display: block;
    background: var(--card-bg);
    padding: 30px;
    border-radius: 12px;
    text-decoration: none;
    color: inherit;
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
    text-align: center;
}

.tool-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-hover);
    border-color: var(--primary-color);
}

.tool-icon {
    font-size: 2.5rem;
    margin-bottom: 15px;
    color: var(--primary-color);
}

.tool-card h3 {
    margin-bottom: 10px;
    font-size: 1.2rem;
}

.tool-card p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

h2 {
    font-size: 1.8rem;
    margin-bottom: 25px;
    color: var(--text-color);
}

.tool-container {
    background: var(--card-bg);
    padding: 30px;
    border-radius: 12px;
    border: 1px solid var(--border-color);
}

.input-group {
    margin-bottom: 20px;
}

.input-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
    color: var(--text-color);
}

textarea,
input[type="text"],
input[type="datetime-local"] {
    width: 100%;
    padding: 12px 15px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    font-size: 14px;
    font-family: inherit;
    transition: border-color 0.2s;
}

textarea {
    min-height: 150px;
    resize: vertical;
}

textarea:focus,
input[type="text"]:focus,
input[type="datetime-local"]:focus {
    outline: none;
    border-color: var(--primary-color);
}

.button-group {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-bottom: 20px;
}

button {
    padding: 10px 20px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 14px;
    cursor: pointer;
    transition: background 0.2s;
}

button:hover {
    background: var(--primary-hover);
}

button:active {
    transform: scale(0.98);
}

.timestamp-converter {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.converter-item {
    display: flex;
    align-items: center;
    gap: 15px;
    flex-wrap: wrap;
}

.converter-item label {
    min-width: 150px;
    font-weight: 500;
}

.converter-item input {
    flex: 1;
    min-width: 200px;
}

footer {
    background: var(--card-bg);
    padding: 20px 0;
    text-align: center;
    border-top: 1px solid var(--border-color);
    color: var(--text-secondary);
}

@media (max-width: 768px) {
    header h1 {
        font-size: 1.8rem;
    }

    .nav-list {
        padding: 10px;
    }

    .tool-grid {
        grid-template-columns: 1fr;
    }

    .converter-item {
        flex-direction: column;
        align-items: stretch;
    }

    .converter-item label {
        min-width: auto;
    }
}