:root {
    --primary-color: #4f46e5;
    --primary-hover: #4338ca;
    --bg-color: #f9fafb;
    --text-color: #111827;
    --text-muted: #6b7280;
    --white: #ffffff;
    --border-color: #e5e7eb;
    --success-color: #10b981;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    display: flex;
    justify-content: center;
    padding: 2rem 1rem;
}

.container {
    width: 100%;
    max-width: 600px;
    background: var(--white);
    padding: 2rem;
    border-radius: 1rem;
    box-shadow: var(--shadow);
}

header {
    text-align: center;
    margin-bottom: 2rem;
}

header h1 {
    margin: 0;
    font-size: 2rem;
    font-weight: 800;
    color: var(--primary-color);
}

header p {
    color: var(--text-muted);
    margin-top: 0.5rem;
}

.input-group {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 2rem;
}

input[type="text"] {
    flex: 1;
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    font-size: 1rem;
    outline: none;
    transition: border-color 0.2s;
}

input[type="text"]:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

button#addHabitBtn {
    padding: 0.75rem 1.5rem;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 0.5rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.2s;
}

button#addHabitBtn:hover {
    background-color: var(--primary-hover);
}

.habit-item {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    padding: 1rem;
    border: 1px solid var(--border-color);
    border-radius: 0.75rem;
    margin-bottom: 1rem;
    transition: transform 0.1s;
}

.habit-main {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.habit-info {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.habit-name {
    font-weight: 600;
    font-size: 1.1rem;
}

.checkbox {
    width: 1.5rem;
    height: 1.5rem;
    cursor: pointer;
    accent-color: var(--success-color);
}

.streak-container {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-muted);
    font-size: 0.875rem;
}

.days-grid {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: 0.5rem;
    text-align: center;
}

.day-cell {
    font-size: 0.75rem;
    padding: 0.25rem;
    border-radius: 0.25rem;
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    color: var(--text-muted);
}

.day-cell.completed {
    background-color: var(--success-color);
    color: white;
    border-color: var(--success-color);
}

.delete-btn {
    background: none;
    border: none;
    color: #ef4444;
    cursor: pointer;
    font-size: 0.875rem;
    padding: 0;
    opacity: 0.6;
    transition: opacity 0.2s;
}

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