:root {
    /* Light Mode Colors */
    --bg-primary: #ffffff;
    --bg-secondary: #f7f7f5; /* Notion-like sidebar gray */
    --bg-hover: #efefef;
    --bg-active: #e0e0e0;
    --text-primary: #37352f;
    --text-secondary: #787774;
    --text-tertiary: #9b9a97;
    --border-color: #e9e9e8;
    --accent-color: #2383e2;
    --accent-hover: #1d6fbf;
    --danger-color: #eb5757;
    --danger-hover: #c93b3b;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.05);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.05);
    
    /* Spacing */
    --spacing-xs: 4px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --spacing-2xl: 48px;

    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
    --font-size-sm: 14px;
    --font-size-base: 16px;
    --font-size-lg: 18px;
    --font-size-xl: 24px;
    --font-size-2xl: 32px;
    
    /* Radius */
    --radius-sm: 4px;
    --radius-md: 6px;
    --radius-lg: 8px;
}

[data-theme="dark"] {
    /* Dark Mode Colors */
    --bg-primary: #191919;
    --bg-secondary: #202020;
    --bg-hover: #2c2c2c;
    --bg-active: #373737;
    --text-primary: #d4d4d4;
    --text-secondary: #9b9a97;
    --text-tertiary: #6b6b6b;
    --border-color: #2f2f2f;
    --accent-color: #4ea7fc;
    --accent-hover: #3b8fd9;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.3);
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: background-color 0.2s ease, color 0.2s ease;
    -webkit-font-smoothing: antialiased;
}

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

/* Typography */
h1, h2, h3 {
    font-weight: 600;
    line-height: 1.3;
    color: var(--text-primary);
}

/* Buttons */
button {
    cursor: pointer;
    font-family: inherit;
    border: none;
    background: none;
    transition: all 0.2s ease;
    color: var(--text-secondary);
    display: inline-flex;
    align-items: center;
    justify-content: center;
}

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

button:active {
    background-color: var(--bg-active);
    transform: translateY(1px);
}

.btn-primary {
    background-color: var(--accent-color) !important;
    color: white !important;
    font-weight: 500;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
}

.btn-primary:hover {
    background-color: var(--accent-hover) !important;
    box-shadow: var(--shadow-md);
}

.btn-danger {
    color: var(--danger-color) !important;
}

.btn-danger:hover {
    background-color: rgba(235, 87, 87, 0.1) !important;
    color: var(--danger-hover) !important;
}

/* Inputs */
input, textarea {
    font-family: inherit;
    background-color: transparent;
    border: 1px solid transparent; /* Invisible border by default for cleaner look, or subtle */
    color: var(--text-primary);
    padding: var(--spacing-sm);
    border-radius: var(--radius-sm);
    transition: all 0.2s ease;
    width: 100%;
}

input:hover, textarea:hover {
    background-color: var(--bg-hover);
}

input:focus, textarea:focus {
    outline: none;
    background-color: transparent;
    border-color: var(--accent-color); /* Or just box-shadow */
    box-shadow: 0 0 0 2px rgba(35, 131, 226, 0.2);
}

input[type="checkbox"] {
    width: 18px;
    height: 18px;
    accent-color: var(--accent-color);
    cursor: pointer;
}

/* Layout Utilities */
.hidden { display: none !important; }
.flex { display: flex; }
.flex-col { display: flex; flex-direction: column; }
.items-center { align-items: center; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.gap-xs { gap: var(--spacing-xs); }
.gap-sm { gap: var(--spacing-sm); }
.gap-md { gap: var(--spacing-md); }
.gap-lg { gap: var(--spacing-lg); }
.p-xs { padding: var(--spacing-xs); }
.p-sm { padding: var(--spacing-sm); }
.p-md { padding: var(--spacing-md); }
.p-lg { padding: var(--spacing-lg); }
.rounded { border-radius: var(--radius-sm); }
.w-full { width: 100%; }
.h-full { height: 100%; }
.text-sm { font-size: var(--font-size-sm); }
.text-lg { font-size: var(--font-size-lg); }
.text-xl { font-size: var(--font-size-xl); }
.text-2xl { font-size: var(--font-size-2xl); }
.font-bold { font-weight: 600; }
.text-secondary { color: var(--text-secondary); }
.text-danger { color: var(--danger-color); }
.bg-primary { background-color: var(--bg-primary); }
.bg-secondary { background-color: var(--bg-secondary); }
.border-b { border-bottom: 1px solid var(--border-color); }
.border-t { border-top: 1px solid var(--border-color); }
.shadow-md { box-shadow: var(--shadow-md); }
.truncate { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.cursor-pointer { cursor: pointer; }
.relative { position: relative; }
.absolute { position: absolute; }
.z-10 { z-index: 10; }
.z-50 { z-index: 50; }
.inset-0 { top: 0; right: 0; bottom: 0; left: 0; }

/* Specific Component Styles */

/* Login */
.login-container {
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color) !important;
    transition: transform 0.3s ease;
}
.login-container:hover {
    transform: translateY(-2px);
}

/* Sidebar */
.sidebar {
    transition: width 0.3s ease, transform 0.3s ease;
}

.item-link {
    transition: background-color 0.1s ease, color 0.1s ease;
    color: var(--text-secondary);
    font-weight: 500;
}

.item-link:hover {
    background-color: var(--bg-hover);
    color: var(--text-primary);
}

.item-link.bg-hover { /* Active state */
    background-color: var(--bg-active);
    color: var(--text-primary);
}

/* Editors */
#item-title {
    font-size: 2.5rem;
    font-weight: 700;
    padding: var(--spacing-sm) 0;
    margin-bottom: var(--spacing-md);
}

#item-title:hover {
    background-color: transparent;
}

#item-title:focus {
    box-shadow: none;
}

.todo-text {
    transition: color 0.2s ease;
}

.todo-check {
    border-radius: 4px;
}

.group:hover .opacity-0 {
    opacity: 1;
}

.opacity-0 {
    opacity: 0;
    transition: opacity 0.2s ease;
}

/* Scrollbar */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-secondary);
}

/* Mobile Responsiveness */
@media (max-width: 768px) {
    #app {
        flex-direction: column;
    }

    .sidebar {
        width: 100% !important;
        height: auto;
        border-right: none;
        border-bottom: 1px solid var(--border-color);
        display: none; /* Hidden by default on mobile */
    }

    .sidebar.open {
        display: flex;
        height: 100%;
        position: absolute;
        z-index: 20;
        background-color: var(--bg-secondary);
    }

    #mobile-menu-btn {
        display: block !important;
    }
}

#mobile-menu-btn {
    display: none;
}