:root {
    /* Core color palette */
    --primary-color: #6200ee;
    --primary-variant: #3700b3;
    --secondary-color: #03dac6;
    --secondary-variant: #018786;
    --background-color: #f5f5f5;
    --surface-color: #ffffff;
    --error-color: #b00020;
    --success-color: #4caf50;
    
    /* Text colors */
    --on-primary: #ffffff;
    --on-secondary: #000000;
    --on-background: #121212;
    --on-surface: #121212;
    --on-error: #ffffff;
    
    /* Neutrals */
    --grey-50: #fafafa;
    --grey-100: #f5f5f5;
    --grey-200: #eeeeee;
    --grey-300: #e0e0e0;
    --grey-400: #bdbdbd;
    --grey-500: #9e9e9e;
    --grey-600: #757575;
    --grey-700: #616161;
    --grey-800: #424242;
    --grey-900: #212121;
    
    /* Shades for heatmap */
    --primary-100: rgb(98, 0, 238, 0.1);
    --primary-200: rgb(98, 0, 238, 0.2);
    --primary-300: rgb(98, 0, 238, 0.3);
    --primary-400: rgb(98, 0, 238, 0.4);
    --primary-500: rgb(98, 0, 238, 0.5);
    --primary-600: rgb(98, 0, 238, 0.6);
    --primary-700: rgb(98, 0, 238, 0.7);
    --primary-800: rgb(98, 0, 238, 0.8);
    --primary-900: rgb(98, 0, 238, 0.9);
    
    /* Dimensions */
    --grid-gap: 8px;
    --date-size: 40px;
    --sidebar-width: 280px;
    --border-radius-sm: 8px;
    --border-radius-md: 12px;
    --border-radius-lg: 16px;
    --border-radius-xl: 24px;
    
    /* Elevations (shadows) */
    --elevation-1: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
    --elevation-2: 0 3px 6px rgba(0,0,0,0.15), 0 2px 4px rgba(0,0,0,0.12);
    --elevation-3: 0 10px 20px rgba(0,0,0,0.15), 0 3px 6px rgba(0,0,0,0.10);
    --elevation-4: 0 14px 28px rgba(0,0,0,0.25), 0 10px 10px rgba(0,0,0,0.22);
    --elevation-5: 0 19px 38px rgba(0,0,0,0.30), 0 15px 12px rgba(0,0,0,0.22);
    
    /* Animation durations */
    --animation-short: 0.15s;
    --animation-medium: 0.3s;
    --animation-long: 0.5s;
}

@media (prefers-color-scheme: dark) {
    :root {
        --background-color: #121212;
        --surface-color: #1e1e1e;
        --on-background: #ffffff;
        --on-surface: #ffffff;
        --grey-50: #212121;
        --grey-100: #424242;
        --grey-200: #616161;
        --grey-300: #757575;
        --grey-400: #9e9e9e;
        --grey-500: #bdbdbd;
        --grey-600: #e0e0e0;
        --grey-700: #eeeeee;
        --grey-800: #f5f5f5;
        --grey-900: #fafafa;
    }
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background-color: var(--background-color);
    color: var(--on-background);
    min-height: 100vh;
    font-size: 16px;
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Layout */
.app-container {
    position: relative;
    min-height: 100vh;
    display: flex;
}

/* Sidebar */
.sidebar {
    width: var(--sidebar-width);
    background-color: var(--surface-color);
    padding: 24px 16px;
    box-shadow: var(--elevation-2);
    display: flex;
    flex-direction: column;
    position: fixed;
    top: 0;
    left: 0;
    height: 100vh;
    z-index: 10;
    transform: translateX(0);
    transition: transform var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
}

.sidebar.hidden {
    transform: translateX(-100%);
}

.logo-container {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 40px;
}

.logo {
    width: 32px;
    height: 32px;
    border-radius: 8px;
}

.habits-list-container {
    flex-grow: 1;
    margin-bottom: 24px;
}

.habits-list-container h2 {
    margin-bottom: 16px;
    color: var(--primary-color);
    font-size: 1.25rem;
}

.habits-list {
    list-style: none;
    margin-top: 16px;
}

.habit-item {
    padding: 12px 16px;
    margin-bottom: 8px;
    background-color: var(--background-color);
    border-radius: var(--border-radius-md);
    cursor: pointer;
    transition: all var(--animation-short) ease;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.habit-item:hover {
    background-color: var(--grey-100);
    transform: translateY(-2px);
}

.habit-item.active {
    background-color: var(--primary-color);
    color: var(--on-primary);
}

.habit-item .habit-actions {
    opacity: 0;
    transition: opacity var(--animation-short) ease;
    display: flex;
    gap: 8px;
}

.habit-item:hover .habit-actions {
    opacity: 1;
}

.sidebar-footer {
    padding-top: 16px;
    border-top: 1px solid var(--grey-200);
    text-align: center;
    color: var(--grey-500);
    font-size: 0.875rem;
}

/* Main content */
.main-content {
    flex: 1;
    padding: 24px;
    margin-left: var(--sidebar-width);
    display: flex;
    flex-direction: column;
    gap: 24px;
}

/* Mobile header */
.mobile-header {
    display: none;
    align-items: center;
    justify-content: space-between;
    padding: 16px 0;
    margin-bottom: 16px;
}

.menu-toggle {
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    width: 24px;
    height: 20px;
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 0;
}

.menu-toggle span {
    display: block;
    width: 100%;
    height: 2px;
    background-color: var(--on-background);
    transition: all 0.3s ease;
    transform-origin: left center;
}

.menu-toggle.active span:nth-child(1) {
    transform: rotate(45deg);
}

.menu-toggle.active span:nth-child(2) {
    opacity: 0;
}

.menu-toggle.active span:nth-child(3) {
    transform: rotate(-45deg);
}

/* Habit selector container */
.habit-selector-container {
    display: flex;
    align-items: center;
    gap: 12px;
}

.habit-select {
    flex: 1;
    background: var(--surface-color);
    color: var(--on-surface);
    border: 1px solid var(--grey-300);
    padding: 12px 16px;
    border-radius: var(--border-radius-md);
    cursor: pointer;
    font-size: 1rem;
    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='%239e9e9e'%3E%3Cpath d='M7 10l5 5 5-5z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 12px center;
    transition: border-color var(--animation-short) ease, box-shadow var(--animation-short) ease;
}

.habit-select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(98, 0, 238, 0.2);
}

/* Stats card */
.stats-card {
    display: flex;
    gap: 16px;
    background-color: var(--surface-color);
    padding: 24px;
    border-radius: var(--border-radius-lg);
    box-shadow: var(--elevation-1);
    transition: transform var(--animation-short) ease, box-shadow var(--animation-short) ease;
}

.stats-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--elevation-2);
}

.stat-item {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    padding: 16px;
    border-radius: var(--border-radius-md);
    background-color: var(--grey-50);
}

.current-streak {
    background-color: rgba(98, 0, 238, 0.1);
}

.longest-streak {
    background-color: rgba(3, 218, 198, 0.1);
}

.total-days {
    background-color: rgba(76, 175, 80, 0.1);
}

.stat-value {
    font-size: 2.5rem;
    font-weight: 700;
    line-height: 1;
    margin-bottom: 8px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    font-size: 0.875rem;
    color: var(--grey-600);
}

/* Calendar navigation */
.calendar-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 24px;
}

.current-month {
    font-size: 1.5rem;
    font-weight: 600;
    text-align: center;
    flex: 1;
}

.nav-btn {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: var(--surface-color);
    color: var(--on-surface);
    border: none;
    cursor: pointer;
    transition: all var(--animation-short) ease;
    box-shadow: var(--elevation-1);
}

.nav-btn svg {
    fill: currentColor;
}

.nav-btn:hover {
    background-color: var(--primary-color);
    color: var(--on-primary);
    transform: scale(1.05);
    box-shadow: var(--elevation-2);
}

/* Calendar card */
.calendar-card {
    background-color: var(--surface-color);
    border-radius: var(--border-radius-lg);
    padding: 24px;
    box-shadow: var(--elevation-1);
    overflow: hidden;
}

.weekdays {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: var(--grid-gap);
    margin-bottom: 16px;
    text-align: center;
    color: var(--grey-600);
    font-weight: 500;
}

.dates-grid {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: var(--grid-gap);
    animation: fadeIn var(--animation-medium) ease-out;
}

.date {
    aspect-ratio: 1;
    width: var(--date-size);
    height: var(--date-size);
    display: flex;
    align-items: center;
    justify-content: center;
    margin: auto;
    position: relative;
    cursor: pointer;
    border-radius: 50%;
    font-weight: 500;
    transition: all var(--animation-short) cubic-bezier(0.4, 0, 0.2, 1);
    background-color: var(--grey-50);
    user-select: none;
}

.date:hover {
    background-color: var(--grey-200);
    transform: scale(1.1);
    z-index: 1;
}

.date.empty {
    background-color: transparent;
    cursor: default;
}

.date.empty:hover {
    transform: none;
}

.date.today {
    border: 2px solid var(--primary-color);
    font-weight: 700;
    color: var(--primary-color);
}

.date.ticked {
    background-color: var(--primary-color);
    color: var(--on-primary);
    transform: scale(1);
    box-shadow: var(--elevation-1);
}

.date.ticked:hover {
    background-color: var(--primary-variant);
    transform: scale(1.05);
    box-shadow: var(--elevation-2);
}

.date.ticked::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 10px;
    height: 5px;
    border-left: 2px solid var(--on-primary);
    border-bottom: 2px solid var(--on-primary);
    transform: translate(-50%, -70%) rotate(-45deg);
    animation: checkmark var(--animation-short) ease-in-out forwards;
}

/* Year view */
.year-view-card {
    background-color: var(--surface-color);
    border-radius: var(--border-radius-lg);
    padding: 24px;
    box-shadow: var(--elevation-1);
}

.year-view-card h3 {
    margin-bottom: 16px;
    color: var(--grey-700);
}

.year-heatmap {
    display: grid;
    grid-template-columns: repeat(52, 1fr);
    grid-template-rows: repeat(7, 1fr);
    gap: 2px;
    height: 120px;
}

.heatmap-cell {
    width: 100%;
    height: 100%;
    border-radius: 2px;
    transition: all var(--animation-short) ease;
    cursor: pointer;
}

.heatmap-cell:hover {
    transform: scale(1.2);
    z-index: 1;
}

/* Mobile navigation */
.mobile-nav {
    display: none;
    position: fixed;
    bottom: 0;
    left: 0;
    width: 100%;
    background-color: var(--surface-color);
    box-shadow: 0 -2px 10px rgba(0, 0, 0, 0.1);
    z-index: 5;
    flex-direction: row;
    justify-content: space-around;
    padding: 8px 0;
}

.nav-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 4px;
    padding: 8px 16px;
    border-radius: var(--border-radius-md);
    background: transparent;
    border: none;
    color: var(--grey-600);
    cursor: pointer;
    transition: all var(--animation-short) ease;
}

.nav-item svg {
    fill: currentColor;
    width: 24px;
    height: 24px;
}

.nav-item span {
    font-size: 0.75rem;
}

.nav-item.active {
    color: var(--primary-color);
}

/* Mobile panel for habits */
.mobile-panel {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: var(--surface-color);
    z-index: 20;
    transform: translateX(100%);
    transition: transform var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    flex-direction: column;
}

.mobile-panel.active {
    transform: translateX(0);
}

.panel-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px;
    border-bottom: 1px solid var(--grey-200);
}

.panel-content {
    padding: 16px;
    flex-grow: 1;
    overflow-y: auto;
}

/* Buttons */
button {
    font-family: inherit;
    cursor: pointer;
    transition: all var(--animation-short) ease;
}

.btn-primary {
    background-color: var(--primary-color);
    color: var(--on-primary);
    border: none;
    padding: 10px 24px;
    border-radius: var(--border-radius-md);
    font-weight: 500;
    box-shadow: var(--elevation-1);
}

.btn-primary:hover {
    background-color: var(--primary-variant);
    box-shadow: var(--elevation-2);
    transform: translateY(-2px);
}

.btn-secondary {
    background-color: transparent;
    color: var(--primary-color);
    border: 1px solid var(--primary-color);
    padding: 10px 24px;
    border-radius: var(--border-radius-md);
    font-weight: 500;
}

.btn-secondary:hover {
    background-color: rgba(98, 0, 238, 0.1);
    transform: translateY(-2px);
}

.btn-icon {
    display: flex;
    align-items: center;
    gap: 8px;
    border-radius: var(--border-radius-md);
    padding: 10px 16px;
}

.btn-icon-only {
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: var(--on-surface);
    border: none;
    box-shadow: var(--elevation-1);
}

.btn-icon-only:hover {
    background-color: var(--grey-100);
    transform: scale(1.05);
    box-shadow: var(--elevation-2);
}

.btn-text {
    background: transparent;
    border: none;
    color: var(--primary-color);
    padding: 8px 16px;
    font-weight: 500;
}

.btn-text:hover {
    background-color: rgba(98, 0, 238, 0.1);
    border-radius: var(--border-radius-sm);
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 30;
}

.modal.active {
    display: block;
}

.modal-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
}

.modal-content {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%) scale(0.9);
    background-color: var(--surface-color);
    padding: 24px;
    border-radius: var(--border-radius-lg);
    box-shadow: var(--elevation-3);
    width: 90%;
    max-width: 400px;
    opacity: 0;
    transition: all var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
}

.modal.active .modal-content {
    transform: translate(-50%, -50%) scale(1);
    opacity: 1;
}

.modal-content h3 {
    margin-bottom: 16px;
    color: var(--primary-color);
}

.input-group {
    margin-bottom: 24px;
}

.input-group label {
    display: block;
    margin-bottom: 8px;
    color: var(--grey-700);
    font-size: 0.875rem;
}

.input-group input {
    width: 100%;
    padding: 12px 16px;
    border: 1px solid var(--grey-300);
    border-radius: var(--border-radius-md);
    background-color: var(--background-color);
    color: var(--on-background);
    font-size: 1rem;
    transition: border-color var(--animation-short) ease, box-shadow var(--animation-short) ease;
}

.input-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(98, 0, 238, 0.2);
}

.modal-actions {
    display: flex;
    justify-content: flex-end;
    gap: 12px;
}

/* Install prompt */
.install-prompt {
    position: fixed;
    bottom: 24px;
    left: 50%;
    transform: translate(-50%, 200%);
    background-color: var(--surface-color);
    border-radius: var(--border-radius-lg);
    box-shadow: var(--elevation-3);
    z-index: 15;
    transition: transform var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
    opacity: 0;
    display: none;
}

.install-prompt.active {
    transform: translate(-50%, 0);
    opacity: 1;
    display: block;
}

.prompt-content {
    display: flex;
    align-items: center;
    padding: 16px;
    gap: 16px;
}

.prompt-icon svg {
    fill: var(--primary-color);
}

.prompt-text p {
    font-weight: 500;
}

.prompt-actions {
    display: flex;
    gap: 8px;
}

/* Toast notifications */
.toast {
    position: fixed;
    bottom: 24px;
    left: 50%;
    transform: translate(-50%, 100%);
    background-color: var(--surface-color);
    color: var(--on-surface);
    padding: 0;
    border-radius: var(--border-radius-md);
    box-shadow: var(--elevation-3);
    opacity: 0;
    transition: all var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 25;
    overflow: hidden;
}

.toast.active {
    transform: translate(-50%, 0);
    opacity: 1;
}

.toast-content {
    display: flex;
    align-items: center;
    padding: 12px 20px;
    gap: 12px;
}

.toast-icon {
    fill: var(--success-color);
}

.toast-message {
    font-weight: 500;
}

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

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

@keyframes scaleIn {
    from { transform: scale(0.95); opacity: 0; }
    to { transform: scale(1); opacity: 1; }
}

@keyframes slideUp {
    from { transform: translate(-50%, 100%); }
    to { transform: translate(-50%, 0); }
}

@keyframes checkmark {
    0% { transform: translate(-50%, -70%) rotate(-45deg) scale(0); }
    50% { transform: translate(-50%, -70%) rotate(-45deg) scale(1.2); }
    100% { transform: translate(-50%, -70%) rotate(-45deg) scale(1); }
}

/* Month transition animations */
.month-transition-enter {
    opacity: 0;
    transform: translateX(100%);
}

.month-transition-enter-active {
    opacity: 1;
    transform: translateX(0);
    transition: all var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
}

.month-transition-exit {
    opacity: 1;
    transform: translateX(0);
}

.month-transition-exit-active {
    opacity: 0;
    transform: translateX(-100%);
    transition: all var(--animation-medium) cubic-bezier(0.4, 0, 0.2, 1);
}

/* Responsive design */
@media (max-width: 1200px) {
    .sidebar {
        width: 240px;
    }
    
    .main-content {
        margin-left: 240px;
        padding: 20px;
    }
}

@media (max-width: 992px) {
    .app-container {
        flex-direction: column;
    }
    
    .sidebar {
        display: none;
    }
    
    .main-content {
        margin-left: 0;
        padding: 16px;
    }
    
    .mobile-header {
        display: flex;
    }
    
    .mobile-nav {
        display: flex;
    }
    
    .year-view-card {
        margin-bottom: 72px; /* Space for mobile navigation */
    }
}

@media (max-width: 768px) {
    :root {
        --date-size: 36px;
    }
    
    .stats-card {
        flex-direction: column;
        gap: 12px;
    }
    
    .stat-item {
        padding: 12px;
    }
    
    .stat-value {
        font-size: 2rem;
    }
}

@media (max-width: 576px) {
    :root {
        --date-size: 32px;
    }
    
    .app-container {
        padding: 0;
    }
    
    .main-content {
        padding: 12px;
        gap: 16px;
    }
    
    .calendar-card {
        padding: 16px;
    }
    
    .weekdays span {
        font-size: 0.75rem;
    }
    
    .calendar-nav {
        gap: 16px;
    }
    
    .current-month {
        font-size: 1.25rem;
    }
    
    .year-heatmap {
        height: 100px;
    }
}

@media (max-width: 360px) {
    :root {
        --date-size: 28px;
    }
    
    .main-content {
        padding: 8px;
        gap: 12px;
    }
    
    .calendar-card {
        padding: 12px;
    }
    
    .nav-item {
        padding: 6px 8px;
    }
    
    .habit-select {
        padding: 10px 12px;
    }
}

@media (any-hover: hover) {
    /* Apply hover effects only on devices that can hover */
    .date:hover {
        transform: scale(1.1);
        z-index: 1;
    }
}

/* Utility classes */
.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    border: 0;
}