:root {
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --danger-color: #ef4444;
    --success-color: #22c55e;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --radius-lg: 1rem;
    --radius-md: 0.5rem;
    --transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 2rem;
}

.app-container {
    background: var(--card-bg);
    width: 100%;
    max-width: 500px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    padding: 2rem;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    animation: fadeIn 0.5s ease-out;
}

header {
    text-align: center;
}

h1 {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    letter-spacing: -0.025em;
}

.date-display {
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
}

.input-group {
    display: flex;
    gap: 0.75rem;
    position: relative;
}

input[type="text"] {
    flex: 1;
    padding: 0.875rem 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    font-family: inherit;
    font-size: 1rem;
    transition: var(--transition);
    outline: none;
}

input[type="text"]:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

#addTaskBtn {
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--radius-md);
    width: 3.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: var(--transition);
}

#addTaskBtn:hover {
    background-color: var(--primary-hover);
    transform: translateY(-1px);
}

#addTaskBtn:active {
    transform: translateY(0);
}

.task-list-container {
    min-height: 200px;
    position: relative;
}

.task-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.task-item {
    display: flex;
    align-items: center;
    padding: 1rem;
    background: white;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    transition: var(--transition);
    animation: slideIn 0.3s ease-out;
    gap: 1rem;
}

.task-item:hover {
    border-color: var(--primary-color);
    transform: translateX(4px);
    box-shadow: var(--shadow-sm);
}

.task-item.completed {
    background-color: #f1f5f9;
    border-color: transparent;
}

.task-item.completed .task-text {
    text-decoration: line-through;
    color: var(--text-secondary);
}

.checkbox-wrapper {
    position: relative;
    width: 24px;
    height: 24px;
    cursor: pointer;
}

.custom-checkbox {
    width: 100%;
    height: 100%;
    border: 2px solid var(--border-color);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.checkbox-wrapper input {
    position: absolute;
    opacity: 0;
    cursor: pointer;
    height: 0;
    width: 0;
}

.checkbox-wrapper input:checked + .custom-checkbox {
    background-color: var(--success-color);
    border-color: var(--success-color);
}

.checkbox-wrapper input:checked + .custom-checkbox::after {
    content: '';
    width: 6px;
    height: 10px;
    border: solid white;
    border-width: 0 2px 2px 0;
    transform: rotate(45deg);
    margin-top: -2px;
}

.task-text {
    flex: 1;
    font-size: 1rem;
    color: var(--text-primary);
    transition: var(--transition);
}

.delete-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 0.5rem;
    opacity: 0;
    transition: var(--transition);
    border-radius: var(--radius-md);
}

.task-item:hover .delete-btn {
    opacity: 1;
}

.delete-btn:hover {
    color: var(--danger-color);
    background-color: #fee2e2;
}

.empty-state {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
    color: var(--text-secondary);
    width: 100%;
    display: none;
}

.empty-state.visible {
    display: block;
}

footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
    color: var(--text-secondary);
    font-size: 0.875rem;
}

.text-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    font-size: 0.875rem;
    transition: var(--transition);
}

.text-btn:hover {
    color: var(--primary-color);
    text-decoration: underline;
}

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

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

@keyframes slideOut {
    to { opacity: 0; transform: translateX(20px); }
}