:root {
    /* Light Mode Variables */
    --bg-main: #F8FAFC;
    --bg-card: #FFFFFF;
    --bg-bottom-nav: #FFFFFF;
    --text-primary: #0F172A;
    --text-secondary: #64748B;
    --border-color: #E2E8F0;
    --primary: #4F46E5;
    --primary-hover: #4338CA;
    --success: #10B981;
    --danger: #EF4444;
    --warning: #F59E0B;
    --shadow: 0 4px 6px -1px rgba(0,0,0,0.1), 0 -2px 10px rgba(0,0,0,0.05);
    --modal-overlay: rgba(15, 23, 42, 0.5);
}

[data-theme="dark"] {
    /* Dark Mode Variables */
    --bg-main: #0F172A;
    --bg-card: #1E293B;
    --bg-bottom-nav: #1E293B;
    --text-primary: #F8FAFC;
    --text-secondary: #94A3B8;
    --border-color: #334155;
    --primary: #6366F1;
    --primary-hover: #818CF8;
    --success: #10B981;
    --danger: #EF4444;
    --warning: #FBBF24;
    --shadow: 0 10px 15px -3px rgba(0,0,0,0.5), 0 -2px 10px rgba(0,0,0,0.3);
    --modal-overlay: rgba(0, 0, 0, 0.7);
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-main);
    color: var(--text-primary);
    overflow: hidden;
    transition: background-color 0.3s, color 0.3s;
}

/* Typography & Base */
h1, h2, h3 { color: var(--text-primary); font-weight: 600; }
a, button { font-family: 'Inter', sans-serif; cursor: pointer; }

/* Buttons */
.btn-primary {
    background: var(--primary);
    color: #FFF;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: 0.5rem;
    font-weight: 600;
    transition: all 0.2s;
}
.btn-primary:hover { background: var(--primary-hover); transform: translateY(-1px); }
.btn-secondary {
    background: transparent;
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    padding: 0.75rem 1.5rem;
    border-radius: 0.5rem;
    font-weight: 500;
    transition: all 0.2s;
}
.btn-secondary:hover { background: var(--border-color); }
.btn-danger { background: var(--danger); }
.btn-danger:hover { background: #DC2626; }
.icon-btn {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    width: 40px; height: 40px;
    border-radius: 50%;
    display: flex; align-items: center; justify-content: center;
    transition: all 0.2s;
}
.icon-btn:hover { background: var(--bg-card); color: var(--text-primary); }
.icon-btn-small {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    border-radius: 0.25rem;
    padding: 0.4rem 0.75rem;
    font-weight: 500;
    transition: all 0.2s;
}
.icon-btn-small:hover { color: var(--primary); border-color: var(--primary); }

/* Layout */
.app-container {
    display: flex;
    flex-direction: column;
    height: 100vh;
}
.app-container.hidden { display: none !important; }

/* Main Content */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    padding: 1.5rem 1.5rem 6rem 1.5rem; /* Bottom padding for nav */
    background-color: var(--bg-main);
    overflow: hidden;
    position: relative;
    max-width: 800px;
    margin: 0 auto;
    width: 100%;
}
.header-top {
    display: flex; justify-content: space-between; align-items: center;
    margin-bottom: 1rem;
}
.main-header h1 { font-size: 2rem; }
.theme-icon { width: 24px; height: 24px; }
.theme-icon.hidden { display: none; }

.header-actions { display: flex; gap: 1rem; margin-bottom: 1.5rem; flex-wrap: wrap;}
.search-input, .filter-select {
    padding: 0.6rem 1rem;
    border-radius: 0.5rem;
    border: 1px solid var(--border-color);
    background: var(--bg-card);
    color: var(--text-primary);
    outline: none;
    flex: 1;
}
.search-input:focus, .filter-select:focus { border-color: var(--primary); }

/* Progress */
.progress-wrapper { margin-bottom: 1.5rem; }
#progress-text { font-size: 0.875rem; color: var(--text-secondary); margin-bottom: 0.5rem; display: block; }
.progress-bar {
    height: 6px;
    background: var(--border-color);
    border-radius: 3px;
    overflow: hidden;
}
.progress-fill {
    height: 100%; background: var(--primary);
    width: 0%; transition: width 0.4s ease;
}

/* Todos */
.todo-container { flex: 1; overflow-y: auto; padding-right: 0.5rem; padding-bottom: 2rem; }
.todo-list { list-style: none; }
.todo-item {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 0.75rem;
    padding: 1rem;
    margin-bottom: 1rem;
    display: flex; align-items: flex-start; gap: 1rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.02);
    transition: transform 0.2s, box-shadow 0.2s, opacity 0.3s;
    cursor: grab;
    position: relative;
}
.todo-item:active { cursor: grabbing; }
.todo-item.dragging { opacity: 0.5; box-shadow: none; }
.todo-item.completed .todo-content { opacity: 0.6; }
.todo-item.completed .todo-title { text-decoration: line-through; }
.todo-item.overdue { border-left: 4px solid var(--danger); }

/* Custom Checkbox */
.checkbox {
    width: 24px; height: 24px;
    border: 2px solid var(--border-color);
    border-radius: 50%;
    cursor: pointer;
    flex-shrink: 0;
    display: flex; align-items: center; justify-content: center;
    transition: all 0.2s;
    margin-top: 0.1rem;
}
.checkbox:hover { border-color: var(--primary); }
.todo-item.completed .checkbox { background: var(--success); border-color: var(--success); }
.checkbox::after {
    content: '';
    width: 6px; height: 12px;
    border: solid white;
    border-width: 0 2px 2px 0;
    transform: rotate(45deg);
    opacity: 0;
    margin-top: -2px;
}
.todo-item.completed .checkbox::after { opacity: 1; }

.todo-content { flex: 1; }
.todo-title { font-size: 1.1rem; font-weight: 500; margin-bottom: 0.25rem; transition: all 0.3s; }
.todo-desc { font-size: 0.9rem; color: var(--text-secondary); margin-bottom: 0.5rem; }
.todo-meta { display: flex; flex-wrap: wrap; gap: 0.5rem 1rem; font-size: 0.8rem; color: var(--text-secondary); }
.todo-meta span { display: flex; align-items: center; gap: 0.25rem; }
.priority-high { color: var(--danger); }
.priority-medium { color: var(--warning); }
.priority-low { color: var(--success); }

.todo-actions { display: flex; gap: 0.25rem; }
.action-btn { background: none; border: none; color: var(--text-secondary); cursor: pointer; padding: 0.5rem; border-radius: 0.25rem; }
.action-btn:hover { color: var(--primary); background: var(--bg-main); }
.action-btn.delete:hover { color: var(--danger); }

/* FAB */
.fab {
    position: absolute;
    bottom: 6rem; right: 1.5rem;
    width: 60px; height: 60px;
    border-radius: 50%;
    background: var(--primary);
    color: white;
    border: none;
    font-size: 2rem;
    display: flex; align-items: center; justify-content: center;
    box-shadow: 0 4px 14px rgba(79, 70, 229, 0.4);
    cursor: pointer;
    transition: transform 0.2s;
    z-index: 50;
}
.fab:hover { transform: scale(1.05); }

/* Bottom Navigation */
.bottom-nav {
    position: fixed;
    bottom: 0; left: 0; right: 0;
    background: var(--bg-bottom-nav);
    display: flex;
    justify-content: space-around;
    padding: 0.75rem 0.5rem;
    border-top: 1px solid var(--border-color);
    box-shadow: var(--shadow);
    z-index: 60;
}
.nav-item {
    background: none; border: none;
    display: flex; flex-direction: column; align-items: center; gap: 0.25rem;
    color: var(--text-secondary);
    font-size: 0.75rem;
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 0.5rem;
    transition: all 0.2s;
}
.nav-item:hover { color: var(--primary); }
.nav-item.active { color: var(--primary); font-weight: 600; }
.nav-icon { font-size: 1.25rem; }

/* Modals & Overlays */
.overlay, .modal {
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: var(--modal-overlay);
    display: flex; justify-content: center; align-items: center;
    z-index: 100;
    transition: opacity 0.3s;
}
.hidden { display: none !important; }
.active { display: flex !important; }

.pin-card, .modal-content, .lists-card {
    background: var(--bg-card);
    padding: 1.5rem;
    border-radius: 1rem;
    box-shadow: 0 20px 25px -5px rgba(0,0,0,0.1);
    width: 90%;
    max-width: 500px;
    max-height: 90vh;
    display: flex;
    flex-direction: column;
    animation: fadeIn 0.2s ease-out;
    box-sizing: border-box;
}
.modal-content { padding: 2rem; }

/* Lists View Overlay */
.lists-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 1.5rem; }
.lists-content { flex: 1; overflow-y: auto; overflow-x: hidden; margin-bottom: 1.5rem; width: 100%; }
.custom-cat-list { list-style: none; margin-bottom: 1.5rem; width: 100%; padding: 0; }
.custom-cat-list li {
    display: flex; justify-content: space-between; align-items: center;
    padding: 0.75rem;
    background: var(--bg-main);
    border-radius: 0.5rem;
    margin-bottom: 0.5rem;
    border: 1px solid var(--border-color);
    box-sizing: border-box;
    width: 100%;
}
.cat-name-container { flex: 1; display: flex; align-items: center; cursor: pointer; font-weight: 500; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; margin-right: 0.5rem; }
.cat-actions { display: flex; gap: 0.25rem; flex-shrink: 0; }
.add-category-wrapper { display: flex; gap: 0.5rem; width: 100%; box-sizing: border-box; }
.add-category-wrapper input { flex: 1; padding: 0.75rem; border-radius: 0.5rem; border: 1px solid var(--border-color); background: var(--bg-main); color: var(--text-primary); outline: none; width: 100%; box-sizing: border-box; }
.add-category-wrapper input:focus { border-color: var(--primary); }
.lists-footer { border-top: 1px solid var(--border-color); padding-top: 1rem; text-align: center; }

/* Forms */
.form-group { margin-bottom: 1.25rem; }
.form-group label { display: block; margin-bottom: 0.5rem; font-size: 0.875rem; color: var(--text-secondary); font-weight: 500; }
.form-group input, .form-group textarea, .form-group select {
    width: 100%;
    padding: 0.75rem;
    border-radius: 0.5rem;
    border: 1px solid var(--border-color);
    background: var(--bg-main);
    color: var(--text-primary);
    font-family: inherit;
    outline: none;
    transition: border-color 0.2s;
}
.form-group input:focus, .form-group textarea:focus, .form-group select:focus { border-color: var(--primary); }
.form-group textarea { resize: vertical; min-height: 80px; }
.form-row { display: flex; gap: 1rem; }
.form-row .form-group { flex: 1; }
.modal-actions { display: flex; justify-content: flex-end; gap: 1rem; margin-top: 1.5rem; }

/* PIN specific */
#pin-input {
    text-align: center; letter-spacing: 0.5rem; font-size: 1.25rem; background: var(--bg-main);
    border: 2px solid var(--border-color); color: var(--text-primary); width: 100%; padding: 1rem; border-radius: 0.5rem; margin-bottom: 1rem;
}
#pin-submit { width: 100%; }
.error-msg { color: var(--danger); margin-top: 1rem; font-size: 0.875rem; min-height: 1.2rem; text-align: center; }

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

@media (max-width: 480px) {
    .header-actions { flex-direction: column; }
    .form-row { flex-direction: column; gap: 0; }
}