/* Engineering Knowledge Website - Main Styles */
:root {
    --primary-blue: #1565C0;
    --secondary-blue: #0D47A1;
    --light-blue: #42A5F5;
    --accent-orange: #FF6F00;
    --dark-orange: #E65100;
    --gray-900: #212121;
    --gray-700: #424242;
    --gray-500: #757575;
    --gray-300: #BDBDBD;
    --gray-100: #F5F5F5;
    --white: #FFFFFF;
    --shadow: 0 2px 10px rgba(0,0,0,0.1);
    --shadow-lg: 0 4px 20px rgba(0,0,0,0.15);
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--gray-700);
    background: var(--gray-100);
}

a {
    text-decoration: none;
    color: var(--primary-blue);
}

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

/* Header */
header {
    background: linear-gradient(135deg, var(--secondary-blue), var(--primary-blue));
    color: var(--white);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: var(--shadow);
}

header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--white);
    display: flex;
    align-items: center;
    gap: 10px;
}

.logo i {
    color: var(--accent-orange);
}

nav ul {
    display: flex;
    list-style: none;
    gap: 2rem;
}

nav a {
    color: var(--white);
    font-weight: 500;
    transition: color 0.3s;
    padding: 0.5rem 1rem;
    border-radius: 4px;
}

nav a:hover, nav a.active {
    background: rgba(255,255,255,0.1);
    color: var(--accent-orange);
}

.mobile-menu {
    display: none;
    font-size: 1.5rem;
    cursor: pointer;
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, var(--secondary-blue), var(--light-blue));
    color: var(--white);
    padding: 5rem 0;
    text-align: center;
}

.hero h1 {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.hero p {
    font-size: 1.3rem;
    margin-bottom: 2rem;
    opacity: 0.9;
}

.btn {
    display: inline-block;
    padding: 0.8rem 2rem;
    border-radius: 5px;
    font-weight: 600;
    transition: all 0.3s;
    cursor: pointer;
    border: none;
}

.btn-primary {
    background: var(--accent-orange);
    color: var(--white);
}

.btn-primary:hover {
    background: var(--dark-orange);
    transform: translateY(-2px);
}

.btn-secondary {
    background: var(--white);
    color: var(--primary-blue);
}

.btn-secondary:hover {
    background: var(--gray-100);
}

/* Sections */
.section {
    padding: 4rem 0;
}

.section-title {
    text-align: center;
    margin-bottom: 3rem;
}

.section-title h2 {
    font-size: 2.5rem;
    color: var(--gray-900);
    margin-bottom: 0.5rem;
}

.section-title p {
    color: var(--gray-500);
    font-size: 1.1rem;
}

/* Cards Grid */
.cards-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
}

.card {
    background: var(--white);
    border-radius: 10px;
    padding: 2rem;
    box-shadow: var(--shadow);
    transition: transform 0.3s, box-shadow 0.3s;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.card-icon {
    width: 60px;
    height: 60px;
    background: linear-gradient(135deg, var(--primary-blue), var(--light-blue));
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 1rem;
    color: var(--white);
    font-size: 1.8rem;
}

.card h3 {
    color: var(--gray-900);
    margin-bottom: 0.5rem;
}

.card p {
    color: var(--gray-500);
    margin-bottom: 1rem;
}

.card-link {
    color: var(--accent-orange);
    font-weight: 600;
}

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

.tool-card {
    background: var(--white);
    border-radius: 8px;
    padding: 1.5rem;
    box-shadow: var(--shadow);
    border-left: 4px solid var(--primary-blue);
    transition: all 0.3s;
}

.tool-card:hover {
    border-left-color: var(--accent-orange);
    transform: translateX(5px);
}

.tool-card h4 {
    color: var(--gray-900);
    margin-bottom: 0.5rem;
}

.tool-card p {
    color: var(--gray-500);
    font-size: 0.9rem;
}

.tool-card .badge {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background: var(--gray-100);
    color: var(--gray-700);
    border-radius: 20px;
    font-size: 0.8rem;
    margin-top: 0.5rem;
}

/* Articles */
.article-card {
    background: var(--white);
    border-radius: 10px;
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: transform 0.3s;
}

.article-card:hover {
    transform: translateY(-5px);
}

.article-card img {
    width: 100%;
    height: 200px;
    object-fit: cover;
}

.article-card .content {
    padding: 1.5rem;
}

.article-card .meta {
    color: var(--gray-500);
    font-size: 0.85rem;
    margin-bottom: 0.5rem;
}

.article-card h3 {
    color: var(--gray-900);
    margin-bottom: 0.5rem;
}

.article-card p {
    color: var(--gray-500);
}

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

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    color: var(--gray-700);
    font-weight: 500;
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: 0.8rem;
    border: 1px solid var(--gray-300);
    border-radius: 5px;
    font-size: 1rem;
    transition: border-color 0.3s;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--primary-blue);
}

/* Calculator Styles */
.calculator {
    background: var(--white);
    border-radius: 10px;
    padding: 2rem;
    box-shadow: var(--shadow);
}

.calculator h2 {
    color: var(--gray-900);
    margin-bottom: 1.5rem;
    padding-bottom: 1rem;
    border-bottom: 2px solid var(--gray-100);
}

.calc-result {
    background: linear-gradient(135deg, var(--primary-blue), var(--light-blue));
    color: var(--white);
    padding: 1.5rem;
    border-radius: 8px;
    margin-top: 1.5rem;
    text-align: center;
}

.calc-result .value {
    font-size: 2rem;
    font-weight: 700;
}

.calc-result .unit {
    font-size: 1rem;
    opacity: 0.9;
}

/* Footer */
footer {
    background: var(--gray-900);
    color: var(--white);
    padding: 3rem 0 1rem;
}

.footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-col h4 {
    color: var(--accent-orange);
    margin-bottom: 1rem;
}

.footer-col ul {
    list-style: none;
}

.footer-col a {
    color: var(--gray-300);
    display: block;
    padding: 0.3rem 0;
    transition: color 0.3s;
}

.footer-col a:hover {
    color: var(--accent-orange);
}

.footer-bottom {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid var(--gray-700);
    color: var(--gray-500);
}

/* 404 */
.error-page {
    text-align: center;
    padding: 5rem 0;
}

.error-page h1 {
    font-size: 8rem;
    color: var(--primary-blue);
}

.error-page h2 {
    font-size: 2rem;
    color: var(--gray-700);
    margin-bottom: 1rem;
}

/* Tool Detail Page */
.tool-detail {
    background: var(--white);
    border-radius: 10px;
    padding: 2rem;
    box-shadow: var(--shadow);
    margin-top: 2rem;
}

.tool-detail h1 {
    color: var(--gray-900);
    margin-bottom: 1rem;
}

.tool-detail .description {
    color: var(--gray-500);
    margin-bottom: 2rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--gray-100);
}

.tool-inputs {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

/* Article Page */
.article-content {
    background: var(--white);
    border-radius: 10px;
    padding: 3rem;
    box-shadow: var(--shadow);
}

.article-content img {
    width: 100%;
    max-height: 400px;
    object-fit: cover;
    border-radius: 10px;
    margin: 2rem 0;
}

.article-content h2 {
    color: var(--gray-900);
    margin: 2rem 0 1rem;
}

.article-content p {
    margin-bottom: 1rem;
    line-height: 1.8;
}

/* Responsive */
@media (max-width: 768px) {
    nav ul {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--secondary-blue);
        flex-direction: column;
        padding: 1rem;
        gap: 0.5rem;
    }

    nav ul.active {
        display: flex;
    }

    .mobile-menu {
        display: block;
    }

    .hero h1 {
        font-size: 2rem;
    }

    .section-title h2 {
        font-size: 2rem;
    }

    .cards-grid, .tools-grid {
        grid-template-columns: 1fr;
    }
}

/* Utility Classes */
.text-center { text-align: center; }
.mt-1 { margin-top: 1rem; }
.mt-2 { margin-top: 2rem; }
.mb-1 { margin-bottom: 1rem; }
.mb-2 { margin-bottom: 2rem; }