/* -------------------------------------------------------------
 * CORE DESIGN SYSTEM & VARIABLES
 * ------------------------------------------------------------- */
:root {
    --bg-main: #0b0f19;
    --bg-surface: #131b2e;
    --bg-surface-hover: #1e2942;
    --border-color: #24324f;
    --border-color-hover: #3b4f76;
    
    --color-text-primary: #f8fafc;
    --color-text-secondary: #94a3b8;
    --color-text-muted: #64748b;
    
    --color-primary: #4f46e5;
    --color-primary-light: #6366f1;
    --color-primary-glow: rgba(99, 102, 241, 0.15);
    
    --color-success: #10b981;
    --color-success-glow: rgba(16, 185, 129, 0.2);
    
    --color-warning: #f59e0b;
    --color-danger: #ef4444;
    
    --font-sans: 'Outfit', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-mono: 'Fira Code', monospace;
    
    --sidebar-width: 320px;
    --header-height: 80px;
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.3), 0 4px 6px -2px rgba(0, 0, 0, 0.15);
    --shadow-glow: 0 0 20px rgba(99, 102, 241, 0.3);
    
    --transition-fast: 0.15s ease;
    --transition-normal: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

/* -------------------------------------------------------------
 * RESET & BASE STYLES
 * ------------------------------------------------------------- */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-sans);
    background-color: var(--bg-main);
    color: var(--color-text-primary);
    overflow: hidden;
    height: 100vh;
    width: 100vw;
    -webkit-font-smoothing: antialiased;
}

button {
    font-family: inherit;
    cursor: pointer;
    border: none;
    background: none;
    outline: none;
    color: inherit;
}

/* -------------------------------------------------------------
 * APP LAYOUT
 * ------------------------------------------------------------- */
.app-container {
    display: flex;
    height: 100vh;
    width: 100vw;
    position: relative;
}

/* -------------------------------------------------------------
 * SIDEBAR (Left panel)
 * ------------------------------------------------------------- */
.sidebar {
    width: var(--sidebar-width);
    background-color: var(--bg-surface);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: flex-col;
    flex-shrink: 0;
    z-index: 100;
    transition: transform var(--transition-normal);
    display: flex;
    flex-direction: column;
}

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

.sidebar-header {
    height: var(--header-height);
    padding: 0 1.5rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    border-bottom: 1px solid var(--border-color);
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--color-primary-light);
    letter-spacing: 0.2px;
    line-height: 1.2;
}

.logo svg {
    stroke: var(--color-primary-light);
}

.toggle-sidebar-btn {
    display: none; /* Mobile only */
    padding: 0.5rem;
    border-radius: 8px;
    color: var(--color-text-secondary);
    transition: var(--transition-fast);
}

.toggle-sidebar-btn:hover {
    background-color: var(--bg-surface-hover);
    color: var(--color-text-primary);
}

.import-section {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.custom-file-upload {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    background-color: var(--color-primary);
    color: white;
    padding: 0.75rem 1rem;
    border-radius: 10px;
    font-weight: 600;
    font-size: 0.9rem;
    cursor: pointer;
    transition: var(--transition-normal);
    box-shadow: var(--shadow-sm);
}

.custom-file-upload:hover {
    background-color: var(--color-primary-light);
    box-shadow: 0 0 15px rgba(99, 102, 241, 0.4);
    transform: translateY(-1px);
}

.custom-file-upload input[type="file"] {
    display: none;
}

.drag-drop-text {
    font-size: 0.75rem;
    color: var(--color-text-muted);
    text-align: center;
    border: 1px dashed var(--border-color);
    padding: 0.5rem;
    border-radius: 6px;
    background-color: rgba(11, 15, 25, 0.3);
}

.tasks-menu {
    flex: 1;
    overflow-y: auto;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

/* Custom scrollbar for task menu */
.tasks-menu::-webkit-scrollbar {
    width: 6px;
}
.tasks-menu::-webkit-scrollbar-track {
    background: transparent;
}
.tasks-menu::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 3px;
}
.tasks-menu::-webkit-scrollbar-thumb:hover {
    background: var(--border-color-hover);
}

.menu-category {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.category-title {
    font-size: 0.8rem;
    font-weight: 700;
    text-transform: uppercase;
    color: var(--color-text-secondary);
    letter-spacing: 1px;
    padding-left: 0.5rem;
    margin-bottom: 0.25rem;
}

.category-list {
    display: flex;
    flex-direction: column;
    gap: 0.35rem;
}

.file-item {
    border-radius: 8px;
    overflow: hidden;
    border: 1px solid rgba(36, 50, 79, 0.4);
    background-color: rgba(19, 27, 46, 0.4);
}

.file-header {
    width: 100%;
    padding: 0.65rem 0.75rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-weight: 500;
    font-size: 0.875rem;
    text-align: left;
    transition: var(--transition-fast);
}

.file-header:hover {
    background-color: var(--bg-surface-hover);
}

.file-name {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.file-header svg.chevron {
    transition: transform var(--transition-normal);
}

.file-item.expanded svg.chevron {
    transform: rotate(90deg);
}

.file-equations {
    display: none;
    border-top: 1px solid var(--border-color);
    background-color: rgba(11, 15, 25, 0.4);
    padding: 0.35rem;
    flex-direction: column;
    gap: 0.25rem;
}

.file-item.expanded .file-equations {
    display: flex;
}

.equation-item {
    width: 100%;
    padding: 0.5rem 0.75rem;
    border-radius: 6px;
    font-family: var(--font-mono);
    font-size: 0.8rem;
    text-align: left;
    display: flex;
    align-items: center;
    justify-content: space-between;
    transition: var(--transition-fast);
}

.equation-item:hover {
    background-color: var(--bg-surface-hover);
    color: var(--color-text-primary);
}

.equation-item.active {
    background-color: var(--color-primary-glow);
    border: 1px solid rgba(99, 102, 241, 0.3);
    color: var(--color-primary-light);
    font-weight: 600;
}

.status-badge {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--color-text-muted);
}

.equation-item.solved .status-badge {
    background-color: var(--color-success);
    box-shadow: 0 0 8px var(--color-success);
}

.sidebar-footer {
    padding: 1rem 1.5rem;
    border-top: 1px solid var(--border-color);
    font-size: 0.75rem;
    color: var(--color-text-muted);
    line-height: 1.4;
    text-align: center;
}

/* -------------------------------------------------------------
 * MAIN CONTENT
 * ------------------------------------------------------------- */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    height: 100%;
    position: relative;
    background-color: var(--bg-main);
}

.main-header {
    height: var(--header-height);
    padding: 0 2rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    border-bottom: 1px solid var(--border-color);
    background-color: rgba(19, 27, 46, 0.3);
    backdrop-filter: blur(8px);
}

.menu-btn {
    display: none; /* Mobile only */
    padding: 0.5rem;
    border-radius: 8px;
    color: var(--color-text-secondary);
}

.task-info h1 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--color-text-primary);
    margin-bottom: 0.15rem;
}

.task-info p {
    font-size: 0.85rem;
    color: var(--color-text-secondary);
}

.top-controls {
    display: flex;
    gap: 0.75rem;
}

.control-btn {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    color: var(--color-text-secondary);
    padding: 0.5rem 0.85rem;
    border-radius: 8px;
    font-size: 0.85rem;
    font-weight: 500;
    transition: var(--transition-fast);
}

.control-btn:hover:not(:disabled) {
    background-color: var(--bg-surface-hover);
    color: var(--color-text-primary);
    border-color: var(--border-color-hover);
}

.control-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

/* -------------------------------------------------------------
 * WORKSPACE & STATES
 * ------------------------------------------------------------- */
.workspace {
    flex: 1;
    position: relative;
    overflow-y: auto;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 2rem;
}

/* Empty State */
.empty-state {
    text-align: center;
    max-width: 450px;
    padding: 2rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.25rem;
}

.empty-icon {
    color: var(--color-primary-light);
    animation: float 4s ease-in-out infinite;
}

.empty-state h2 {
    font-size: 1.5rem;
    font-weight: 700;
}

.empty-state p {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.5;
}

.primary-btn {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-light) 100%);
    color: white;
    font-weight: 600;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    font-size: 0.95rem;
    transition: var(--transition-normal);
    box-shadow: 0 4px 14px rgba(99, 102, 241, 0.3);
}

.primary-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.4);
}

.primary-btn:active {
    transform: translateY(0);
}

.secondary-btn {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    color: var(--color-text-primary);
    font-weight: 600;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    font-size: 0.95rem;
    transition: var(--transition-fast);
}

.secondary-btn:hover {
    background-color: var(--bg-surface-hover);
    border-color: var(--border-color-hover);
}

/* -------------------------------------------------------------
 * SOLVER LAYOUT
 * ------------------------------------------------------------- */
.solver-container {
    width: 100%;
    max-width: 900px;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2rem;
    padding-bottom: 120px; /* Space for the floating arsenal */
}

/* The Big Equation Display Card */
.equation-card {
    background: radial-gradient(100% 100% at 50% 0%, rgba(30, 41, 59, 0.5) 0%, rgba(15, 23, 42, 0.8) 100%);
    border: 1px solid var(--border-color);
    border-radius: 24px;
    width: 100%;
    min-height: 250px;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 3rem 2rem;
    box-shadow: var(--shadow-lg);
    position: relative;
    backdrop-filter: blur(12px);
}

.equation-display {
    display: flex;
    align-items: center;
    justify-content: center;
    flex-wrap: wrap;
    row-gap: 1.5rem;
    column-gap: 0.5rem;
    font-family: var(--font-sans);
    font-size: 3.5rem;
    font-weight: 500;
    user-select: none;
}

.tool-helper-text {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    background-color: rgba(30, 41, 59, 0.4);
    border: 1px solid var(--border-color);
    padding: 0.6rem 1.2rem;
    border-radius: 30px;
    text-align: center;
    transition: all var(--transition-fast);
    letter-spacing: 0.2px;
}

/* -------------------------------------------------------------
 * EQUATION PARTS & MATH RENDERING
 * ------------------------------------------------------------- */

/* A full algebra term (e.g. "3x", "-5", "x/3") */
.math-term {
    display: inline-flex;
    align-items: center;
    position: relative;
    border-radius: 12px;
    padding: 0.25rem 0.5rem;
    transition: all var(--transition-fast);
    cursor: default;
    border: 2px solid transparent;
}

/* Relation operators (=, <, >, <=, >=) */
.math-relation {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0 1rem;
    color: var(--color-primary-light);
    font-weight: 600;
}

/* Plus/Minus connector between terms */
.math-operator {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0 0.25rem;
    color: var(--color-text-muted);
}

/* Sign indicator inside a term (optional) */
.term-sign {
    color: var(--color-text-muted);
    margin-right: 0.1rem;
}

/* Simple term wrapper (e.g. coeff + var) */
.term-body {
    display: flex;
    align-items: center;
}

/* Coefficient digit */
.term-coef {
    transition: all var(--transition-fast);
    border-radius: 4px;
    padding: 0 2px;
}

/* Variable character (e.g., "x") */
.term-var {
    color: var(--color-text-primary);
    font-style: italic;
    font-weight: 600;
}

/* Fraction Rendering */
.term-fraction {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    line-height: 1;
    padding: 0 0.25rem;
}

.fraction-numerator {
    display: flex;
    align-items: center;
    justify-content: center;
    padding-bottom: 4px;
}

.fraction-line {
    width: 100%;
    height: 2px;
    background-color: var(--color-text-primary);
    margin: 2px 0;
}

.fraction-denominator {
    font-size: 2.2rem;
    padding-top: 4px;
    transition: all var(--transition-fast);
    border-radius: 4px;
    padding: 2px 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-family: var(--font-sans);
}

/* -------------------------------------------------------------
 * INTERACTION: ARSENAL TOOL COUPLING
 * ------------------------------------------------------------- */

/* When + or - tool is active, the entire math term is clickable */
body.tool-active-plus .math-term,
body.tool-active-minus .math-term {
    cursor: pointer;
    border-color: rgba(99, 102, 241, 0.2);
    background-color: rgba(99, 102, 241, 0.03);
}

body.tool-active-plus .math-term:hover,
body.tool-active-minus .math-term:hover {
    border-color: var(--color-primary-light);
    background-color: rgba(99, 102, 241, 0.1);
    box-shadow: 0 0 15px rgba(99, 102, 241, 0.2);
    transform: scale(1.03);
}

/* When * tool is active, both coefficients/constants and denominators are clickable */
body.tool-active-multiply .term-coef,
body.tool-active-multiply .fraction-denominator {
    cursor: pointer;
    border: 2px dashed rgba(245, 158, 11, 0.4);
    background-color: rgba(245, 158, 11, 0.05);
    color: var(--color-warning);
    padding: 0 4px;
    border-radius: 4px;
}

body.tool-active-multiply .term-coef:hover,
body.tool-active-multiply .fraction-denominator:hover {
    border-color: var(--color-warning);
    background-color: rgba(245, 158, 11, 0.2);
    box-shadow: 0 0 12px rgba(245, 158, 11, 0.4);
    transform: scale(1.1);
}

/* When / tool is active, both coefficients/constants and denominators are clickable */
body.tool-active-divide .term-coef,
body.tool-active-divide .fraction-denominator {
    cursor: pointer;
    border: 2px dashed rgba(16, 185, 129, 0.4);
    background-color: rgba(16, 185, 129, 0.05);
    color: var(--color-success);
    padding: 0 4px;
    border-radius: 4px;
}

body.tool-active-divide .term-coef:hover,
body.tool-active-divide .fraction-denominator:hover {
    border-color: var(--color-success);
    background-color: rgba(16, 185, 129, 0.2);
    box-shadow: 0 0 12px rgba(16, 185, 129, 0.4);
    transform: scale(1.1);
}

/* Animation for applied operation flying or term combining */
@keyframes term-disappear {
    0% { transform: scale(1); opacity: 1; }
    50% { transform: scale(1.2); opacity: 0.5; filter: blur(2px); }
    100% { transform: scale(0); opacity: 0; }
}

.term-removing {
    animation: term-disappear 0.4s cubic-bezier(0.6, -0.28, 0.735, 0.045) forwards;
}

/* -------------------------------------------------------------
 * SOLUTION STEPS LOG
 * ------------------------------------------------------------- */
.steps-container {
    width: 100%;
    background-color: rgba(19, 27, 46, 0.5);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 1.25rem 1.5rem;
    box-shadow: var(--shadow-md);
}

.steps-container h3 {
    font-size: 0.95rem;
    font-weight: 700;
    text-transform: uppercase;
    color: var(--color-text-secondary);
    letter-spacing: 1px;
    margin-bottom: 0.75rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}

.steps-list {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.step-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-family: var(--font-mono);
    font-size: 0.95rem;
    padding: 0.35rem 0;
    border-bottom: 1px dashed rgba(36, 50, 79, 0.3);
}

.step-row:last-child {
    border-bottom: none;
    font-weight: 700;
    color: var(--color-text-primary);
}

.step-math {
    color: var(--color-text-secondary);
}

.step-row:last-child .step-math {
    color: var(--color-text-primary);
}

.step-op {
    color: var(--color-warning);
    font-weight: 600;
    background-color: rgba(245, 158, 11, 0.1);
    padding: 0.15rem 0.5rem;
    border-radius: 6px;
    font-size: 0.85rem;
}

.step-row:last-child .step-op {
    background-color: rgba(16, 185, 129, 0.1);
    color: var(--color-success);
}

/* -------------------------------------------------------------
 * ARSENAL DOCK (Bottom panel)
 * ------------------------------------------------------------- */
.arsenal-dock {
    position: absolute;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%);
    background: rgba(19, 27, 46, 0.8);
    border: 1px solid var(--border-color);
    border-radius: 20px;
    padding: 0.75rem 1.5rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
    box-shadow: var(--shadow-lg), 0 20px 25px -5px rgba(0, 0, 0, 0.4);
    backdrop-filter: blur(16px);
    z-index: 10;
    width: auto;
}

.arsenal-title {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    color: var(--color-text-secondary);
    letter-spacing: 1.5px;
}

.arsenal-buttons {
    display: flex;
    gap: 0.75rem;
}

.arsenal-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    width: 68px;
    height: 68px;
    background-color: rgba(11, 15, 25, 0.5);
    border: 1px solid var(--border-color);
    border-radius: 14px;
    transition: all var(--transition-normal);
}

.arsenal-btn:hover {
    background-color: var(--bg-surface-hover);
    border-color: var(--color-primary-light);
    transform: translateY(-4px);
    box-shadow: 0 4px 12px rgba(99, 102, 241, 0.15);
}

.arsenal-btn:active {
    transform: translateY(-1px);
}

.arsenal-btn .op-symbol {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 2px;
}

.arsenal-btn .op-name {
    font-size: 0.65rem;
    font-weight: 600;
    text-transform: uppercase;
    color: var(--color-text-muted);
}

.arsenal-btn:hover .op-name {
    color: var(--color-text-secondary);
}

/* Tool specific highlights in active state */
.arsenal-btn.active {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-light) 100%);
    border-color: white;
    color: white;
    box-shadow: var(--shadow-glow);
    transform: translateY(-4px) scale(1.05);
}

.arsenal-btn.active .op-name {
    color: rgba(255, 255, 255, 0.8);
}

/* Operator specific colors when active */
.arsenal-btn[data-op="+"].active {
    box-shadow: 0 0 20px rgba(99, 102, 241, 0.4);
}
.arsenal-btn[data-op="-"].active {
    box-shadow: 0 0 20px rgba(99, 102, 241, 0.4);
}
.arsenal-btn[data-op="*"].active {
    background: linear-gradient(135deg, #d97706 0%, #f59e0b 100%);
    box-shadow: 0 0 20px rgba(245, 158, 11, 0.4);
}
.arsenal-btn[data-op="/"].active {
    background: linear-gradient(135deg, #059669 0%, #10b981 100%);
    box-shadow: 0 0 20px rgba(16, 185, 129, 0.4);
}

/* -------------------------------------------------------------
 * SUCCESS MODAL OVERLAY
 * ------------------------------------------------------------- */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background-color: rgba(11, 15, 25, 0.85);
    backdrop-filter: blur(8px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease;
}

.modal-overlay.active {
    opacity: 1;
    pointer-events: auto;
}

.modal-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: 28px;
    width: 95%;
    max-width: 600px;
    padding: 2.5rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    transform: scale(0.9) translateY(20px);
    transition: transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.modal-overlay.active .modal-card {
    transform: scale(1) translateY(0);
}

.success-icon {
    width: 80px;
    height: 80px;
    background-color: var(--color-success-glow);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--color-success);
    margin-bottom: 1.5rem;
    box-shadow: 0 0 25px var(--color-success-glow);
    animation: pulse-success 2s infinite;
}

.modal-card h2 {
    font-size: 1.75rem;
    font-weight: 800;
    margin-bottom: 1rem;
    background: linear-gradient(to right, #ffffff, #94a3b8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.solution-display {
    background-color: rgba(11, 15, 25, 0.4);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 1.25rem;
    width: 100%;
    margin-bottom: 2rem;
}

.solution-label {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    color: var(--color-text-secondary);
    letter-spacing: 1px;
    margin-bottom: 0.5rem;
}

.solution-math {
    font-family: var(--font-mono);
    font-size: clamp(1.2rem, 4.5vw, 1.9rem);
    font-weight: 700;
    color: var(--color-success);
    margin-bottom: 0.25rem;
    white-space: nowrap;
    overflow-x: auto;
    width: 100%;
}

.solution-interval {
    font-family: var(--font-sans);
    font-size: 1.1rem;
    color: var(--color-text-secondary);
}

.modal-actions {
    display: flex;
    gap: 1rem;
    width: 100%;
}

.modal-actions button {
    flex: 1;
}

/* -------------------------------------------------------------
 * CONFETTI CANVAS
 * ------------------------------------------------------------- */
.confetti-canvas {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 999;
}

/* -------------------------------------------------------------
 * ANIMATIONS
 * ------------------------------------------------------------- */
@keyframes float {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
}

@keyframes pulse-success {
    0% { box-shadow: 0 0 0 0 rgba(16, 185, 129, 0.4); }
    70% { box-shadow: 0 0 0 15px rgba(16, 185, 129, 0); }
    100% { box-shadow: 0 0 0 0 rgba(16, 185, 129, 0); }
}

/* -------------------------------------------------------------
 * RESPONSIVENESS
 * ------------------------------------------------------------- */
@media (max-width: 900px) {
    .toggle-sidebar-btn {
        display: block;
    }
    
    .menu-btn {
        display: block;
    }
    
    .sidebar {
        position: absolute;
        height: 100%;
        transform: translateX(-100%);
    }
    
    .sidebar.active {
        transform: translateX(0);
    }
}

/* Drag and Drop visual indicator */
.main-content.drag-over::after {
    content: "Dateien hier ablegen, um Aufgaben zu laden";
    position: absolute;
    top: 1rem;
    left: 1rem;
    right: 1rem;
    bottom: 1rem;
    background-color: rgba(99, 102, 241, 0.15);
    border: 3px dashed var(--color-primary-light);
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-primary-light);
    backdrop-filter: blur(4px);
    z-index: 1000;
    pointer-events: none;
    transition: all var(--transition-normal);
}