:root {
    --bg-color: #0f172a; 
    --surface-color: rgba(30, 41, 59, 0.7); 
    --surface-solid: rgba(30, 41, 59, 0.95);
    --surface-border: rgba(255, 255, 255, 0.1);
    --primary: #8b5cf6; 
    --primary-hover: #7c3aed; 
    --text-main: #f8fafc; 
    --text-muted: #94a3b8; 
    --success: #10b981; 
    --danger: #ef4444; 
    --font-family: 'Outfit', sans-serif;
    
    /* Dynamic */
    --input-bg: rgba(15, 23, 42, 0.6);
    --item-bg: rgba(255, 255, 255, 0.03);
    --item-border: rgba(255, 255, 255, 0.05);
    --item-bg-hover: rgba(255, 255, 255, 0.05);
    --item-border-hover: rgba(255, 255, 255, 0.1);
    --calendar-icon-filter: invert(1);
    --bg-gradient-1: rgba(139, 92, 246, 0.15);
    --bg-gradient-2: rgba(16, 185, 129, 0.15);
}

body.light-theme {
    --bg-color: #f1f5f9; 
    --surface-color: rgba(255, 255, 255, 0.7); 
    --surface-solid: rgba(255, 255, 255, 0.95);
    --surface-border: rgba(0, 0, 0, 0.1);
    --text-main: #0f172a; 
    --text-muted: #64748b; 
    
    --input-bg: rgba(255, 255, 255, 0.6);
    --item-bg: rgba(0, 0, 0, 0.02);
    --item-border: rgba(0, 0, 0, 0.05);
    --item-bg-hover: rgba(0, 0, 0, 0.05);
    --item-border-hover: rgba(0, 0, 0, 0.1);
    --calendar-icon-filter: invert(0);
    --bg-gradient-1: rgba(139, 92, 246, 0.1);
    --bg-gradient-2: rgba(16, 185, 129, 0.1);
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    background-image: 
        radial-gradient(circle at 15% 50%, var(--bg-gradient-1), transparent 25%),
        radial-gradient(circle at 85% 30%, var(--bg-gradient-2), transparent 25%);
    color: var(--text-main);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 2rem;
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Theme Toggle */
.theme-toggle {
    position: absolute;
    top: 2rem;
    right: 2rem;
    background: var(--surface-color);
    border: 1px solid var(--surface-border);
    color: var(--text-main);
    width: 48px;
    height: 48px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    backdrop-filter: blur(16px);
    transition: all 0.3s ease;
    z-index: 100;
}

.theme-toggle:hover {
    transform: scale(1.1);
    background: var(--item-bg-hover);
}

body.light-theme .sun-icon { display: none; }
body.light-theme .moon-icon { display: block !important; }

/* Existing Layout */
.app-container {
    display: flex;
    gap: 2rem;
    width: 100%;
    max-width: 1600px;
    height: 85vh;
    min-height: 600px;
    margin-top: 4rem;
}

.left-section, .right-section, .middle-section {
    flex: 1;
    background: var(--surface-color);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--surface-border);
    border-radius: 24px;
    padding: 2.5rem;
    display: flex;
    flex-direction: column;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    overflow: hidden;
    position: relative;
    z-index: 1;
    transition: background-color 0.3s ease, border-color 0.3s ease;
}

header h1, header h2 {
    font-weight: 600;
    font-size: 2rem;
    letter-spacing: -0.025em;
    margin-bottom: 0.5rem;
}

header h2 { color: var(--success); }
header h2.focus-title { color: #f59e0b; }
header p { color: var(--text-muted); font-size: 0.95rem; margin-bottom: 2rem; }

/* Input Styles */
#todo-form { margin-bottom: 2rem; }

.input-group {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    align-items: stretch;
}

#todo-input {
    flex: 1 1 100%;
    background: var(--input-bg);
    border: 1px solid var(--surface-border);
    border-radius: 16px;
    padding: 1rem 1.5rem;
    color: var(--text-main);
    font-size: 1rem;
    font-family: inherit;
    transition: all 0.3s ease;
}

.priority-select {
    flex: 1 1 0;
    height: 56px;
    background: var(--input-bg);
    border: 1px solid var(--surface-border);
    border-radius: 16px;
    color: var(--text-main);
    font-size: 0.95rem;
    font-family: inherit;
    padding: 0 1.5rem;
    cursor: pointer;
    outline: none;
    transition: all 0.3s ease;
    -webkit-appearance: none;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='white' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 1rem center;
    background-size: 1em;
    padding-right: 2.5rem;
}

body.light-theme .priority-select {
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='black' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
}

.priority-select:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.2);
}

.priority-select option {
    background: var(--bg-color);
    color: var(--text-main);
}

.date-select {
    flex: 1 1 0;
    height: 56px;
    background: var(--input-bg);
    border: 1px solid var(--surface-border);
    border-radius: 16px;
    color: var(--text-main);
    font-size: 0.95rem;
    font-family: inherit;
    padding: 0 1rem;
    cursor: pointer;
    outline: none;
    transition: all 0.3s ease;
}

.date-select:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.2);
}

::-webkit-calendar-picker-indicator {
    filter: var(--calendar-icon-filter);
    opacity: 0.7;
    cursor: pointer;
}
::-webkit-calendar-picker-indicator:hover { opacity: 1; }

#todo-input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.2);
}

.edit-input {
    width: 100%;
    background: var(--input-bg);
    border: 1px solid var(--primary);
    border-radius: 12px;
    padding: 0.75rem 1rem;
    color: var(--text-main);
    font-size: 1rem;
    font-family: inherit;
    outline: none;
    box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.2);
}

#todo-input::placeholder { color: rgba(148, 163, 184, 0.5); }

#add-btn {
    background: var(--primary);
    color: white;
    border: none;
    border-radius: 16px;
    width: 60px;
    height: 56px;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: all 0.2s ease;
    flex-shrink: 0;
}

#add-btn:hover { background: var(--primary-hover); transform: scale(1.05); }
#add-btn:active { transform: scale(0.95); }

/* Lists and Items */
ul { list-style: none; }

.date-group-header {
    position: sticky;
    top: 0;
    z-index: 10;
    background: var(--surface-solid);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--primary);
    margin: 0 0 1rem 0;
    padding: 1rem 0 0.5rem 0;
    text-align: left;
    border-bottom: 1px solid rgba(139, 92, 246, 0.2);
    letter-spacing: 0.5px;
    transition: background-color 0.3s ease;
}

.group-list { margin-bottom: 1rem; }

.active-todos-container, .focus-todos-container, .completed-todos-container {
    flex: 1 1 0px;
    min-height: 0;
    overflow-y: auto;
    padding-right: 0.5rem;
}

::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--surface-border); border-radius: 10px; }
::-webkit-scrollbar-thumb:hover { background: rgba(148, 163, 184, 0.5); }

.todo-item {
    background: var(--item-bg);
    border: 1px solid var(--item-border);
    border-radius: 16px;
    padding: 1.25rem;
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    animation: slideIn 0.4s ease-out forwards;
    cursor: grab;
}

.todo-item:active { cursor: grabbing; }

.todo-item:hover {
    background: var(--item-bg-hover);
    transform: translateY(-2px);
    border-color: var(--item-border-hover);
}

.todo-content {
    display: flex;
    align-items: center;
    gap: 1rem;
    flex: 1;
    word-break: break-word;
}

.todo-text {
    font-size: 1.05rem;
    line-height: 1.4;
    color: var(--text-main);
}

.completed-item .todo-text {
    color: var(--text-muted);
    text-decoration: line-through;
    text-decoration-color: rgba(148, 163, 184, 0.4);
}

.meta-row {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-top: 0.5rem;
}

.todo-meta {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.completed-date {
    background: rgba(16, 185, 129, 0.15);
    color: var(--success);
    padding: 0.2rem 0.6rem;
    border-radius: 6px;
    font-size: 0.75rem;
    font-weight: 500;
}

.priority-badge {
    font-size: 0.7rem;
    font-weight: 700;
    padding: 0.2rem 0.6rem;
    border-radius: 6px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.priority-3 { background: rgba(239, 68, 68, 0.15); color: var(--danger); border: 1px solid rgba(239, 68, 68, 0.3); }
.priority-2 { background: rgba(245, 158, 11, 0.15); color: #f59e0b; border: 1px solid rgba(245, 158, 11, 0.3); }
.priority-1 { background: rgba(59, 130, 246, 0.15); color: #3b82f6; border: 1px solid rgba(59, 130, 246, 0.3); }

.action-buttons {
    display: flex;
    gap: 0.5rem;
    margin-left: 1rem;
}

.btn-icon {
    background: transparent;
    border: none;
    border-radius: 50%;
    width: 36px;
    height: 36px;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: all 0.2s ease;
    color: var(--text-muted);
}

.btn-complete:hover { color: var(--success); background: rgba(16, 185, 129, 0.1); }
.btn-delete:hover { color: var(--danger); background: rgba(239, 68, 68, 0.1); }

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

.empty-state {
    text-align: center;
    color: var(--text-muted);
    padding: 3rem 0;
    font-size: 0.95rem;
    animation: fadeIn 0.5s ease;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.drag-over {
    border-color: var(--primary) !important;
    background: rgba(139, 92, 246, 0.1) !important;
}

.dragging {
    opacity: 0.5;
    transform: scale(0.98);
}

@media (max-width: 900px) {
    .theme-toggle {
        top: 0.75rem;
        right: 0.75rem;
        width: 40px;
        height: 40px;
    }
    .app-container { 
        flex-direction: column; 
        height: auto; 
        margin-top: 3.5rem; 
        margin-bottom: 2rem; 
        gap: 1.5rem;
    }
    .left-section, .middle-section, .right-section { 
        height: auto;
        min-height: auto;
        max-height: none;
        padding: 1.25rem;
        border-radius: 16px;
    }
    .active-todos-container, .focus-todos-container, .completed-todos-container {
        height: 50vh;
        min-height: 300px;
        max-height: 500px;
        overflow-y: auto;
        flex: none;
    }
    .priority-select, .date-select {
        flex: 1 1 100%;
    }
    #add-btn {
        width: 100%;
        margin-top: 0.25rem;
    }
    .todo-content {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.5rem;
        width: 100%;
    }
    .action-buttons {
        margin-left: 0;
        margin-top: 1rem;
        width: 100%;
        justify-content: flex-end;
    }
    .todo-item {
        flex-direction: column;
        align-items: flex-start;
    }
    body { 
        padding: 0.5rem; 
        align-items: flex-start; 
        justify-content: center; 
    }
}