/* Global Styles & Variables */
:root {
    --primary-color: #5B6AFF; /* Blue-purple */
    --secondary-color: #8C54FF; /* Purple */
    --background-light: #FFFFFF; /* White */
    --background-grey: #F5F7FA; /* Light grey */
    --text-dark: #333333; /* Dark grey */
    --text-medium: #666666; /* Medium grey */
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
    --border-radius: 12px;
    --spacing-unit: 8px;
    --font-family: 'Roboto', '思源黑体', sans-serif;
}

/* Dark theme variables (can be toggled with JS) */
body.dark-theme {
    --primary-color: #7A8AFF; /* Lighter Blue-purple for dark mode */
    --secondary-color: #A070FF; /* Lighter Purple for dark mode */
    --background-light: #1E1E2F; /* Dark background */
    --background-grey: #2A2A3D; /* Slightly lighter dark background */
    --text-dark: #E0E0E0; /* Light text for dark mode */
    --text-medium: #B0B0B0; /* Medium light text for dark mode */
    --shadow: 0 4px 12px rgba(255, 255, 255, 0.05);
}

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

body {
    font-family: var(--font-family);
    background-color: var(--background-grey);
    color: var(--text-dark);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Top Navigation Bar */
.top-nav {
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    color: var(--background-light);
    padding: calc(var(--spacing-unit) * 2) calc(var(--spacing-unit) * 3);
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.top-nav .logo {
    font-size: calc(var(--spacing-unit) * 2.5);
    font-weight: 700;
}

.top-nav .search-bar {
    display: flex;
    align-items: center;
    background-color: rgba(255, 255, 255, 0.2);
    border-radius: calc(var(--spacing-unit) * 0.5);
    padding: calc(var(--spacing-unit) * 0.5) var(--spacing-unit);
}

.top-nav .search-bar input {
    background: transparent;
    border: none;
    color: var(--background-light);
    outline: none;
    padding: calc(var(--spacing-unit) * 0.5);
    width: 250px; /* Adjust as needed */
}

.top-nav .search-bar input::placeholder {
    color: rgba(255, 255, 255, 0.7);
}

.top-nav .search-bar button {
    background: transparent;
    border: none;
    color: var(--background-light);
    cursor: pointer;
    padding: calc(var(--spacing-unit) * 0.5);
}

.top-nav .nav-actions {
    display: flex;
    align-items: center;
}

.top-nav .action-btn {
    background: transparent;
    border: none;
    color: var(--background-light);
    cursor: pointer;
    margin-left: calc(var(--spacing-unit) * 2);
    font-size: calc(var(--spacing-unit) * 1.75);
    display: flex;
    align-items: center;
}
.top-nav .action-btn i {
    margin-right: calc(var(--spacing-unit) * 0.5);
}

.top-nav .action-btn:hover {
    opacity: 0.8;
}

.top-nav .user-profile {
    display: flex;
    align-items: center;
    margin-left: calc(var(--spacing-unit) * 2);
    cursor: pointer;
}

.top-nav .user-profile i {
    font-size: calc(var(--spacing-unit) * 2.5);
    margin-right: var(--spacing-unit);
}

/* Main Content Area */
.main-content {
    display: flex;
    padding-top: calc(var(--spacing-unit) * 10); /* Height of top-nav */
    flex-grow: 1;
}

/* Left Sidebar */
.left-sidebar {
    width: 250px;
    background-color: var(--background-light);
    padding: calc(var(--spacing-unit) * 3);
    box-shadow: 2px 0 5px rgba(0,0,0,0.05);
    height: calc(100vh - (var(--spacing-unit) * 10)); /* Full height minus top-nav */
    position: fixed;
    top: calc(var(--spacing-unit) * 10);
    left: 0;
    overflow-y: auto;
    transition: background-color 0.3s ease;
}

.category-list {
    list-style: none;
}

.category-item {
    padding: calc(var(--spacing-unit) * 1.5) var(--spacing-unit);
    margin-bottom: var(--spacing-unit);
    border-radius: calc(var(--spacing-unit) * 0.75);
    cursor: pointer;
    display: flex;
    align-items: center;
    color: var(--text-medium);
    transition: background-color 0.2s ease, color 0.2s ease;
}

.category-item i:first-child { /* Icon before text */
    margin-right: calc(var(--spacing-unit) * 1.5);
    width: 20px; /* Ensure icons align */
    text-align: center;
}

.category-item .category-toggle { /* Chevron icon */
    margin-left: auto;
    transition: transform 0.3s ease;
}

.category-item.active .category-toggle.fa-chevron-down {
    transform: rotate(180deg);
}

.category-item:hover {
    background-color: var(--background-grey);
    color: var(--primary-color);
}

.category-item.active {
    background-color: var(--primary-color);
    color: var(--background-light);
    font-weight: 500;
}
.category-item.active:hover {
    color: var(--background-light); /* Keep text color on hover for active item */
}

.subcategory-list {
    list-style: none;
    padding-left: calc(var(--spacing-unit) * 3); /* Indent subcategories */
    margin-top: calc(var(--spacing-unit) * 0.5);
    margin-bottom: var(--spacing-unit);
}

.subcategory-item {
    padding: var(--spacing-unit) calc(var(--spacing-unit) * 1.5);
    border-radius: calc(var(--spacing-unit) * 0.5);
    cursor: pointer;
    color: var(--text-medium);
    font-size: calc(var(--spacing-unit) * 1.75);
    transition: background-color 0.2s ease, color 0.2s ease;
}

.subcategory-item:hover {
    background-color: var(--background-grey);
    color: var(--primary-color);
}


/* Tool Cards Section */
.tool-cards-section {
    flex-grow: 1;
    padding: calc(var(--spacing-unit) * 3);
    margin-left: 250px; /* Width of left-sidebar */
    background-color: var(--background-grey);
    transition: background-color 0.3s ease;
}

.category-header {
    margin-bottom: calc(var(--spacing-unit) * 3);
}

.category-header h2 {
    font-size: calc(var(--spacing-unit) * 3);
    color: var(--text-dark);
    margin-bottom: var(--spacing-unit);
}

.category-header p {
    font-size: calc(var(--spacing-unit) * 1.75);
    color: var(--text-medium);
}

.tool-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: calc(var(--spacing-unit) * 3);
}

.tool-card {
    background-color: var(--background-light);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: calc(var(--spacing-unit) * 2.5);
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    transition: transform 0.2s ease-in-out, box-shadow 0.2s ease-in-out;
}

.tool-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.12);
}

.tool-card .tool-icon {
    font-size: calc(var(--spacing-unit) * 3.5);
    color: var(--primary-color);
    margin-bottom: calc(var(--spacing-unit) * 1.5);
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-fill-color: transparent;
    padding: var(--spacing-unit);
    border-radius: 50%; /* Make it circular if icon is square-ish */
    display: inline-block; /* To contain the gradient */
}

.tool-card .tool-title {
    font-size: calc(var(--spacing-unit) * 2.25);
    color: var(--text-dark);
    margin-bottom: var(--spacing-unit);
}

.tool-card .tool-description {
    font-size: calc(var(--spacing-unit) * 1.75);
    color: var(--text-medium);
    margin-bottom: calc(var(--spacing-unit) * 2);
    flex-grow: 1; /* Makes description take available space */
}

.tool-button {
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    color: var(--background-light);
    border: none;
    border-radius: calc(var(--spacing-unit) * 0.75);
    padding: calc(var(--spacing-unit) * 1.25) calc(var(--spacing-unit) * 2.5);
    font-size: calc(var(--spacing-unit) * 1.75);
    font-weight: 500;
    cursor: pointer;
    transition: opacity 0.2s ease, transform 0.2s ease;
    align-self: flex-start; /* Align button to the start of the card */
}

.tool-button:hover {
    opacity: 0.9;
    transform: scale(1.02);
}

/* Responsive Design */
@media (max-width: 992px) {
    .left-sidebar {
        width: 220px;
    }
    .tool-cards-section {
        margin-left: 220px;
    }
    .tool-grid {
        grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    }
}

@media (max-width: 768px) {
    .top-nav .search-bar {
        display: none; /* Hide search bar on smaller screens or move it */
    }
    .top-nav .logo {
        font-size: calc(var(--spacing-unit) * 2.2);
    }
    .top-nav .action-btn {
        margin-left: var(--spacing-unit);
        font-size: calc(var(--spacing-unit) * 1.5);
    }
    .top-nav .user-profile i {
        font-size: calc(var(--spacing-unit) * 2.2);
    }

    .main-content {
        flex-direction: column;
        padding-top: calc(var(--spacing-unit) * 8); /* Adjust if top-nav height changes */
    }

    .left-sidebar {
        width: 100%;
        height: auto;
        position: static; /* No longer fixed */
        box-shadow: none;
        border-bottom: 1px solid var(--background-grey);
        overflow-y: visible;
    }

    .category-list {
        display: flex;
        flex-wrap: wrap; /* Allow categories to wrap */
        justify-content: space-around; /* Distribute items */
    }
    .category-item {
        flex-basis: calc(50% - var(--spacing-unit) * 2); /* Two items per row approx */
        margin: var(--spacing-unit);
        justify-content: center; /* Center content in mobile view */
    }
    .category-item i:first-child {
        margin-right: var(--spacing-unit);
    }
    .category-item .category-toggle {
        display: none; /* Hide chevron on mobile for simplicity, or adapt */
    }
    .subcategory-list {
        display: none !important; /* Hide subcategories on mobile for now, or implement differently */
    }

    .tool-cards-section {
        margin-left: 0;
        padding: calc(var(--spacing-unit) * 2);
    }

    .tool-grid {
        grid-template-columns: 1fr; /* Single column on small screens */
        gap: calc(var(--spacing-unit) * 2);
    }
}

@media (max-width: 480px) {
    .top-nav {
        padding: var(--spacing-unit) calc(var(--spacing-unit) * 1.5);
    }
    .top-nav .logo {
        font-size: calc(var(--spacing-unit) * 2);
    }
    .top-nav .nav-actions {
        /* Could simplify further, e.g., icons only */
    }
    .top-nav .action-btn span {
        display: none; /* Show only icons for language/theme on very small screens */
    }
    .top-nav .action-btn i {
        margin-right: 0;
    }
    .category-item {
        flex-basis: 100%; /* One item per row on very small screens */
    }
}

/* Smooth Scroll */
html {
    scroll-behavior: smooth;
}