/* ==========================================================================
   1. RESET & DARK THEME VARIABLES
   ========================================================================== */
*,
*::before,
*::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg-main: #0a0f1d;
    --primary-gradient: linear-gradient(135deg, #2563eb 0%, #3b82f6 100%);
    --accent-color: #38bdf8;
    --accent-glow: rgba(56, 189, 248, 0.25);
    --success-color: #10b981;
    --danger-color: #ef4444;
    --warning-color: #f59e0b;
    --edit-color: #06b6d4;
    
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    
    --card-bg: rgba(17, 24, 39, 0.85);
    --card-border: rgba(255, 255, 255, 0.08);
    --input-bg: rgba(15, 23, 42, 0.8);
    --input-border: rgba(255, 255, 255, 0.12);
    
    --shadow-dark: 0 20px 50px rgba(0, 0, 0, 0.6);
    --radius-lg: 20px;
    --radius-md: 12px;
    --radius-sm: 8px;
    --transition-smooth: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ==========================================================================
   2. BODY & BACKGROUND
   ========================================================================== */
body {
    font-family: 'Inter', 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
    position: relative;
    overflow-x: hidden;
    color: var(--text-main);
    background-color: var(--bg-main);
}

.background-animation {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(-45deg, #020617, #0f172a, #1e1b4b, #090d16);
    background-size: 400% 400%;
    animation: gradient 15s ease infinite;
    z-index: -1;
}

@keyframes gradient {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}

/* ==========================================================================
   3. CONTAINER & APP CARD
   ========================================================================== */
.container {
    width: 100%;
    max-width: 680px;
    z-index: 10;
}

.todo-app {
    background: var(--card-bg);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--card-border);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-dark);
    padding: 40px;
    animation: slideIn 0.5s ease-out;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ==========================================================================
   4. HEADER & PROGRESS BAR
   ========================================================================== */
.header {
    text-align: center;
    margin-bottom: 25px;
    border-bottom: 1px solid var(--card-border);
    padding-bottom: 20px;
}

h1 {
    color: #ffffff;
    text-shadow: 0 0 15px var(--accent-glow);
    text-align: center;
    margin-bottom: 6px;
    font-size: 2.5em;
    font-weight: 800;
    letter-spacing: -0.5px;
}

.subtitle {
    color: var(--accent-color);
    font-size: 13px;
    letter-spacing: 2px;
    text-transform: uppercase;
    font-weight: 600;
}

.progress-section {
    margin-bottom: 25px;
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: rgba(255, 255, 255, 0.05);
    border-radius: 20px;
    overflow: hidden;
    margin-bottom: 8px;
    border: 1px solid rgba(255, 255, 255, 0.05);
}

.progress-fill {
    height: 100%;
    background: var(--primary-gradient);
    box-shadow: 0 0 10px var(--accent-glow);
    width: 0%;
    transition: width 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    border-radius: 20px;
}

.progress-text {
    font-size: 13px;
    color: var(--accent-color);
    font-weight: 700;
    text-align: right;
    display: block;
}

/* ==========================================================================
   5. INPUT & BUTTONS
   ========================================================================== */
.input-container {
    display: flex;
    gap: 12px;
    margin-bottom: 20px;
}

.input-wrapper {
    flex: 1;
    display: flex;
    align-items: center;
    background: var(--input-bg);
    border: 1px solid var(--input-border);
    border-radius: var(--radius-md);
    padding: 0 16px;
    transition: var(--transition-smooth);
}

.input-wrapper:focus-within {
    border-color: var(--accent-color);
    box-shadow: 0 0 15px var(--accent-glow);
}

.input-wrapper i {
    color: var(--accent-color);
    margin-right: 12px;
    font-size: 18px;
}

.todo-input {
    flex: 1;
    padding: 14px 0;
    border: none;
    background: transparent;
    font-size: 15px;
    outline: none;
    color: var(--text-main);
    font-weight: 500;
}

.todo-input::placeholder {
    color: #475569;
}

.add-btn {
    padding: 14px 24px;
    background: var(--primary-gradient);
    color: white;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: 15px;
    font-weight: 600;
    transition: var(--transition-smooth);
    display: flex;
    align-items: center;
    gap: 8px;
    box-shadow: 0 4px 15px rgba(37, 99, 235, 0.4);
}

.add-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(56, 189, 248, 0.5);
}

/* Filter Controls */
.filter-buttons {
    display: flex;
    gap: 8px;
    margin-bottom: 20px;
    justify-content: center;
    flex-wrap: wrap;
}

.filter-btn {
    padding: 8px 18px;
    border: 1px solid var(--input-border);
    background: var(--input-bg);
    border-radius: 30px;
    cursor: pointer;
    font-size: 14px;
    transition: var(--transition-smooth);
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 6px;
    color: var(--text-muted);
}

.filter-btn:hover {
    border-color: var(--accent-color);
    color: var(--accent-color);
}

.filter-btn.active {
    background: var(--primary-gradient);
    color: white;
    border-color: transparent;
    box-shadow: 0 0 12px var(--accent-glow);
}

/* ==========================================================================
   6. TODO LIST & ITEM STYLES
   ========================================================================== */
.todo-list {
    list-style: none;
    margin-bottom: 25px;
    max-height: 400px;
    overflow-y: auto;
    padding-right: 4px;
}

.todo-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 14px 16px;
    background: rgba(15, 23, 42, 0.6);
    border-left: 4px solid var(--accent-color);
    border-radius: var(--radius-md);
    margin-bottom: 10px;
    transition: var(--transition-smooth);
    border-top: 1px solid var(--card-border);
    border-right: 1px solid var(--card-border);
    border-bottom: 1px solid var(--card-border);
}

.todo-item:hover {
    transform: translateX(4px);
    background: rgba(30, 41, 59, 0.8);
}

.todo-item.completed {
    background: rgba(15, 23, 42, 0.3);
    border-left-color: var(--success-color);
    opacity: 0.6;
}

.todo-item.completed .todo-text {
    text-decoration: line-through;
    color: #64748b;
}

.checkbox {
    width: 20px;
    height: 20px;
    cursor: pointer;
    accent-color: var(--accent-color);
    flex-shrink: 0;
}

.todo-text {
    flex: 1;
    color: var(--text-main);
    font-size: 15px;
    word-break: break-word;
    font-weight: 500;
}

/* Task Buttons */
.delete-btn, .edit-btn, .save-btn, .cancel-btn {
    border: none;
    padding: 8px 12px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 13px;
    transition: var(--transition-smooth);
    display: flex;
    align-items: center;
    gap: 4px;
    font-weight: 600;
    color: white;
}

.edit-btn { background: rgba(6, 182, 212, 0.2); color: #22d3ee; border: 1px solid rgba(6, 182, 212, 0.3); }
.edit-btn:hover { background: var(--edit-color); color: white; }

.delete-btn { background: rgba(239, 68, 68, 0.2); color: #f87171; border: 1px solid rgba(239, 68, 68, 0.3); }
.delete-btn:hover { background: var(--danger-color); color: white; }

.save-btn { background: var(--success-color); }
.cancel-btn { background: var(--warning-color); }

.edit-input {
    flex: 1;
    padding: 8px 12px;
    background: var(--input-bg);
    border: 1px solid var(--accent-color);
    border-radius: var(--radius-sm);
    font-size: 14px;
    color: var(--text-main);
    outline: none;
}

/* ==========================================================================
   7. STATS & FOOTER
   ========================================================================== */
.stats-section {
    display: flex;
    gap: 12px;
    padding-top: 20px;
    border-top: 1px solid var(--card-border);
}

.stat-card {
    flex: 1;
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 14px;
    background: var(--input-bg);
    border-radius: var(--radius-md);
    border: 1px solid var(--card-border);
}

.stat-card i {
    font-size: 20px;
    color: var(--accent-color);
}

.stat-value {
    font-size: 20px;
    font-weight: 800;
    color: var(--text-main);
}

.stat-label {
    font-size: 11px;
    color: var(--text-muted);
    margin-top: 2px;
    text-transform: uppercase;
    font-weight: 700;
}

.clear-btn {
    background: rgba(239, 68, 68, 0.15);
    color: #f87171;
    border: 1px solid rgba(239, 68, 68, 0.3);
    padding: 12px 18px;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition-smooth);
    font-weight: 600;
}

.clear-btn:hover {
    background: var(--danger-color);
    color: white;
}

/* Scrollbar */
.todo-list::-webkit-scrollbar { width: 6px; }
.todo-list::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.2);
    border-radius: 10px;
}

/* Responsive */
@media (max-width: 640px) {
    .todo-app { padding: 24px; }
    .input-container, .stats-section { flex-direction: column; }
    .add-btn { width: 100%; justify-content: center; }
}