.container-main{max-width:900px;margin:0 auto;padding:var(--spacing-xl) var(--container-padding-x)}.page-title{font-size:var(--font-size-3xl);font-weight:700;color:var(--primary);margin:0;letter-spacing:-.5px}.subtitle{color:var(--text-secondary);font-weight:600;margin-top:var(--spacing-xs);font-size:var(--font-size-sm)}.game-header{display:flex;flex-direction:column;gap:var(--spacing-md);margin-bottom:var(--spacing-lg)}@media(min-width:768px){.game-header{flex-direction:row;justify-content:space-between;align-items:flex-start}}.controls-group{display:flex;flex-direction:column;gap:var(--spacing-sm);width:100%}@media(min-width:640px){.controls-group{flex-direction:row;width:auto;gap:var(--spacing-md)}}.video-link{display:inline-flex;align-items:center;gap:var(--spacing-sm);font-size:var(--font-size-base);font-weight:600;color:var(--primary);text-decoration:none;transition:all var(--transition-normal)}.video-link:hover{color:var(--primary-light)}.difficulty-select{padding:var(--spacing-sm) var(--spacing-md);border-radius:var(--radius-lg);font-weight:600;font-size:var(--font-size-base);border:2px solid var(--outline);background:var(--background);color:var(--text-primary);cursor:pointer;transition:all var(--transition-normal);appearance:none;padding-right:var(--spacing-lg);background-image:url("data:image/svg+xml;charset=UTF-8,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23674ea7' 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 var(--spacing-sm) center;background-size:1.5em 1.5em;padding-right:calc(var(--spacing-lg) + .5rem)}.difficulty-select:hover{border-color:var(--primary);background-color:var(--secondary)}.difficulty-select:focus{outline:none;border-color:var(--primary);box-shadow:0 0 0 4px #674ea726}.difficulty-select option{padding:var(--spacing-md);background:var(--background);color:var(--text-primary)}.difficulty-select option:checked{background:linear-gradient(var(--primary),var(--primary));background-color:var(--primary);color:var(--text-on-primary)}.difficulty-option-easy{background:#dcfce7!important;color:#166534!important}.difficulty-option-easy:checked{background:#10b981!important;color:#fff!important}.difficulty-option-medium{background:#fef3c7!important;color:#b45309!important}.difficulty-option-medium:checked{background:#f59e0b!important;color:#fff!important}.difficulty-option-hard{background:#fee2e2!important;color:#991b1b!important}.difficulty-option-hard:checked{background:#ef4444!important;color:#fff!important}.btn-primary{background:var(--primary);color:var(--text-on-primary);padding:var(--spacing-md) var(--spacing-lg);border:none;border-radius:var(--radius-xl);font-weight:700;cursor:pointer;transition:all var(--transition-normal);white-space:nowrap}.btn-primary:hover{background:var(--primary-light);transform:translateY(-2px);box-shadow:0 8px 20px #674ea74d}.btn-primary:active{transform:translateY(0)}.btn-large{padding:var(--spacing-md) var(--spacing-lg);font-size:var(--font-size-sm);width:100%}@media(min-width:640px){.btn-large{width:auto}}.btn-check{padding:var(--spacing-md) var(--spacing-lg);font-size:var(--font-size-base);min-width:200px}.btn-secondary{background:var(--surface);color:var(--text-primary);padding:var(--spacing-md) var(--spacing-lg);border:2px solid var(--outline);border-radius:var(--radius-xl);font-weight:700;font-size:var(--font-size-sm);cursor:pointer;transition:all var(--transition-normal);width:100%}@media(min-width:640px){.btn-secondary{width:auto}}.btn-secondary:hover{background:var(--outline);border-color:var(--primary)}.instruction-box{padding:var(--spacing-md) var(--spacing-lg);border-radius:var(--radius-xl);text-align:center;font-weight:700;font-size:var(--font-size-sm);border:2px solid var(--outline);margin-bottom:var(--spacing-lg);transition:all var(--transition-normal);width:100%;word-wrap:break-word;overflow-wrap:break-word}.instruction-warning{background:#fee2e2;color:#991b1b;border-color:#fecaca}.instruction-success{background:#dcfce7;color:#166534;border-color:#bbf7d0}.instruction-info{background:var(--secondary);color:#6b21a8;border-color:#ddd6fe}.instruction-hard{background:#f3e8ff;color:#6b21a8;border-color:#e9d5ff}.game-area{margin-bottom:var(--spacing-lg)}.game-container{display:flex;justify-content:center;align-items:center;padding:var(--spacing-lg) 0;gap:var(--spacing-lg);position:relative}.minus-symbol{font-size:3.5rem;color:#cbd5e1;font-weight:700;display:none}@media(min-width:768px){.minus-symbol{display:block;position:absolute;left:-40px}}.math-grid{display:flex;flex-direction:row-reverse;gap:2px;justify-content:center;flex-wrap:wrap;font-family:Arial,Calibri,Trebuchet MS,sans-serif}.math-font{font-family:Arial,Calibri,Trebuchet MS,sans-serif}.digit-column{display:flex;flex-direction:column;align-items:center;width:90px;position:relative}.button-container{height:44px;display:flex;align-items:center;margin-bottom:var(--spacing-sm)}.button-spacer{height:36px;margin-bottom:var(--spacing-sm)}.digit-main{font-size:4rem;margin-bottom:var(--spacing-xs);color:var(--text-primary);font-weight:700;transition:all var(--transition-normal);line-height:1}.digit-sub{font-size:4rem;margin-bottom:var(--spacing-sm);color:var(--text-primary);font-weight:700;line-height:1}.digit-line{width:100%;height:3px;background:var(--text-primary);border-radius:2px;margin-bottom:var(--spacing-sm)}.strikethrough{position:relative;color:var(--text-disabled)}.strikethrough:after{content:"";position:absolute;top:50%;left:-10%;width:120%;height:3px;background:var(--error);transform:rotate(-45deg);border-radius:2px;opacity:.8}.borrowed-val{font-size:1.75rem;color:var(--error);height:40px;font-weight:700;display:flex;align-items:center;justify-content:center;transition:all var(--transition-normal);line-height:1}.input-result{width:80px;height:90px;text-align:center;font-size:2.5rem;border:3px solid var(--outline);border-radius:var(--radius-lg);background:var(--background);transition:all var(--transition-normal);margin-top:var(--spacing-xs);font-family:Arial,Calibri,Trebuchet MS,sans-serif;font-weight:700;color:var(--text-primary);line-height:1}.input-result::-webkit-outer-spin-button,.input-result::-webkit-inner-spin-button{-webkit-appearance:none;margin:0}.input-result:focus{outline:none;border-color:var(--primary);background:var(--secondary);box-shadow:0 0 0 4px #674ea726}.btn-toggle-action{font-size:.6rem;padding:var(--spacing-xs) var(--spacing-xs);border-radius:var(--radius-lg);cursor:pointer;font-weight:700;transition:all var(--transition-normal);text-transform:uppercase;width:80px;height:32px;display:flex;align-items:center;justify-content:center;text-align:center;border:2px solid}.state-borrow{background:#dbeafe;color:#0c4a6e;border-color:#bfdbfe}.state-borrow:hover:not(.btn-disabled){background:var(--primary);color:var(--text-on-primary);border-color:var(--primary);transform:translateY(-1px)}.state-return{background:#fee2e2;color:#7f1d1d;border-color:#fecaca}.state-return:hover{background:var(--error);color:var(--text-on-primary);border-color:var(--error);transform:translateY(-1px)}.btn-disabled{opacity:.5;cursor:not-allowed;pointer-events:none}.button-group{display:flex;flex-direction:column;gap:var(--spacing-sm);justify-content:center;align-items:center;margin-top:var(--spacing-lg)}@media(min-width:640px){.button-group{flex-direction:row;gap:var(--spacing-md)}}.feedback-box{text-align:center;font-weight:700;padding:var(--spacing-lg) var(--spacing-xl);border-radius:var(--radius-xl);border:2px solid;font-size:var(--font-size-base);margin-top:var(--spacing-lg);transition:all var(--transition-normal)}.feedback-success{background:#dcfce7;color:#166534;border-color:#86efac}.feedback-error{background:#fee2e2;color:#991b1b;border-color:#fecaca}.feedback-warning{background:#fef3c7;color:#b45309;border-color:#fcd34d}.hidden{display:none}.highlight-error{color:var(--error)!important;animation:shake .5s ease-in-out}.hard-mode-display{text-align:center;font-size:2rem;margin:var(--spacing-lg) 0}.hard-number{margin-bottom:var(--spacing-md);font-size:4rem;font-weight:700;color:var(--text-primary);line-height:1.2}.hard-divider{border-top:4px solid var(--text-primary);padding-top:var(--spacing-md);margin:var(--spacing-md) 0}.hard-inputs{display:flex;flex-direction:row-reverse;gap:var(--spacing-md);justify-content:center;flex-wrap:wrap;margin-top:var(--spacing-lg)}@keyframes shake{0%,to{transform:translate(0)}25%{transform:translate(-4px)}75%{transform:translate(4px)}}