.btn{cursor:pointer;font-size:.88rem;font-weight:700;font-family:var(--body);border:none;border-radius:8px;padding:.55rem 1.2rem;transition:all .15s}.btn:hover:not(:disabled){transform:translateY(-2px)}.btn:disabled{opacity:.4;cursor:default}.btn-primary{background:var(--blue);color:#fff}.btn-primary:hover:not(:disabled){background:#0a4bbf}.btn-secondary{background:var(--card);color:var(--ink);border:1.5px solid var(--border);padding:.5rem 1rem;font-size:.86rem}.btn-secondary:hover:not(:disabled){border-color:#a0a8b8}.btn-success{background:var(--green);color:#fff}.btn-success:hover:not(:disabled){background:#007a41}.btn-purple{color:#fff;background:#7c3aed;padding:.52rem 1rem;font-size:.84rem;font-weight:800}.btn-purple:hover:not(:disabled){background:#6d28d9}.btn-gold{background:var(--gold);color:var(--ink);font-weight:800}.btn-gold:hover:not(:disabled){background:#ffbe4d}.card{background:var(--card);border:1px solid var(--border);border-radius:12px;margin-bottom:1rem;padding:1.2rem 1.25rem}.frac-in{flex-direction:column;align-items:center;gap:2px;display:inline-flex}.frac-in input{text-align:center;border:2px solid var(--border);background:var(--card);width:54px;color:var(--ink);font-size:1.2rem;font-weight:800;font-family:var(--body);border-radius:8px;outline:none;padding:.28rem .2rem}.frac-in input:focus{border-color:var(--blue)}.frac-in input:disabled{opacity:.5;cursor:not-allowed}.frac-ln{background:var(--ink);border-radius:1px;width:54px;height:2px}.snav{flex-wrap:wrap;flex-shrink:0;justify-content:center;gap:.4rem;max-width:1100px;margin-bottom:1.75rem;margin-left:auto;margin-right:auto;padding:1rem 2rem;display:flex}.sbtn{border:2px solid var(--border);background:var(--card);color:var(--ink2);cursor:pointer;white-space:nowrap;font-size:.78rem;font-weight:800;font-family:var(--body);border-radius:999px;flex-shrink:0;justify-content:center;align-items:center;gap:.35rem;width:156px;padding:.5rem .8rem;transition:background-color .15s,border-color .15s,color .15s;display:inline-flex;position:relative;box-shadow:0 2px 6px #00000012}.sbtn:hover:not(:disabled){border-color:var(--blue);color:var(--blue)}.sbtn:disabled{opacity:.38;cursor:not-allowed}.snum{border:2px solid;border-radius:50%;flex-shrink:0;justify-content:center;align-items:center;width:20px;height:20px;font-size:.7rem;font-weight:900;display:inline-flex}.sbtn[data-step="0"].active{color:#fff;background:#2ec4b6;border-color:#2ec4b6;box-shadow:0 4px 12px #2ec4b659}.sbtn[data-step="1"].active{color:#fff;background:#1865f2;border-color:#1865f2;box-shadow:0 4px 12px #1865f259}.sbtn[data-step="2"].active{color:#fff;background:#ff8c42;border-color:#ff8c42;box-shadow:0 4px 12px #ff8c4259}.sbtn[data-step="3"].active{color:#fff;background:#7c3aed;border-color:#7c3aed;box-shadow:0 4px 12px #7c3aed59}.sbtn[data-step="4"].active{color:#fff;background:#009651;border-color:#009651;box-shadow:0 4px 12px #00965159}.sbtn.active .snum{background:#ffffff40;border-color:#fff9}.sbtn.done{color:#009651;background:var(--green-bg);border-color:#009651}.check-badge{margin-left:-.15rem;font-size:.7rem}.snav-mobile{display:none}@media (width<=768px){.snav{display:none}.snav-mobile{max-width:1100px;margin:0 1rem 1.25rem;display:block}}.snav-mobile-trigger{border:2px solid var(--border);background:var(--card);width:100%;color:var(--ink);cursor:pointer;font-size:.95rem;font-weight:800;font-family:var(--body);border-radius:12px;align-items:center;gap:.5rem;padding:.65rem 1rem;display:flex;box-shadow:0 2px 6px #00000012}.snav-mobile-label{text-align:left;flex:1}.snav-mobile-arrow{color:var(--ink2);transition:transform .2s}.snav-mobile-arrow.open{transform:rotate(180deg)}.snav-mobile-list{border:2px solid var(--border);background:var(--card);border-radius:12px;margin-top:.4rem;overflow:hidden}.snav-mobile-item{border:none;border-bottom:1px solid var(--border);width:100%;color:var(--ink2);cursor:pointer;font-size:.92rem;font-weight:700;font-family:var(--body);background:0 0;align-items:center;gap:.5rem;padding:.75rem 1rem;display:flex}.snav-mobile-item:last-child{border-bottom:none}.snav-mobile-item.active{color:var(--blue);background:var(--blue-bg);font-weight:800}.snav-mobile-item.done{color:#009651}.doodle-wrap{border:2px solid var(--border);background:var(--card);border-radius:12px;margin-top:1.2rem;overflow:hidden}.doodle-toolbar{border-bottom:2px solid var(--border);background:#dfc99a;flex-wrap:wrap;align-items:center;gap:.5rem;padding:.7rem 1rem;display:flex}.doodle-label{color:#5a3c00;font-size:1.3rem;font-weight:800;font-family:var(--body);letter-spacing:.12em;margin-right:.5rem}.doodle-color{border:2.5px solid var(--border);cursor:pointer;background:0 0;border-radius:50%;width:30px;height:30px;padding:0;transition:transform .12s}.doodle-color:hover{transform:scale(1.15)}.doodle-color.active{border-color:var(--blue);transform:scale(1.2)}.doodle-tools{flex-wrap:wrap;align-items:center;gap:.35rem;display:flex}.doodle-tool{border:2px solid var(--border);cursor:pointer;min-height:38px;font-size:.9rem;font-weight:800;font-family:var(--body);color:var(--ink);background:0 0;border-radius:7px;align-items:center;gap:.3rem;padding:.35rem .6rem;display:inline-flex}.doodle-tool.active{border-color:var(--blue);color:var(--blue);background:var(--blue-bg)}.doodle-tool:focus-visible,.doodle-color:focus-visible,.doodle-clear:focus-visible{outline-offset:2px;outline:3px solid #1865f24d}.doodle-clear{border:2px solid var(--border);cursor:pointer;font-size:1rem;font-weight:800;font-family:var(--body);color:var(--ink);background:0 0;border-radius:7px;margin-left:auto;padding:.35rem .85rem}.doodle-clear:hover{border-color:var(--red);color:var(--red)}#doodleCanvas{cursor:crosshair;touch-action:none;width:100%;display:block}@media (width<=700px){.doodle-toolbar{align-items:flex-start}.doodle-label,.doodle-tools{width:100%}.doodle-tool{min-height:44px}.doodle-clear{min-height:44px;margin-left:0}}.number-input{font-family:var(--body);color:var(--ink);border:2px solid var(--border);text-align:center;background:#fff;border-radius:8px;min-width:100px;max-width:150px;padding:.6rem .8rem;font-size:1.3rem;font-weight:700;transition:all .15s}.number-input:focus{border-color:var(--blue);box-shadow:0 0 0 3px var(--blue-bg);outline:none}.number-input:disabled{background:var(--card);opacity:.6;cursor:not-allowed}.number-input::placeholder{color:var(--ink2);opacity:.5}.ptb-spacer{height:60px}@media (width<=640px){.ptb-spacer{height:76px}}.progress-tracker-bar{z-index:40;background:var(--card);border-top:2px solid var(--border);padding:.65rem 1.5rem;position:fixed;bottom:0;left:0;right:0;box-shadow:0 -6px 20px #0000001f}.ptb-inner{flex-wrap:wrap;justify-content:center;align-items:center;gap:1.25rem;max-width:1100px;margin:0 auto;display:flex}.ptb-label{color:var(--ink2);white-space:nowrap;font-size:.9rem;font-weight:700}.ptb-dots{flex-wrap:wrap;justify-content:center;gap:6px;display:flex}.ptb-dot{border:2px solid var(--border);width:24px;height:24px;color:var(--ink2);background:0 0;border-radius:50%;flex-shrink:0;justify-content:center;align-items:center;font-size:.68rem;font-weight:900;display:inline-flex}.ptb-dot.ptb-current{border-color:var(--blue);color:var(--blue);background:var(--blue-bg)}.ptb-dot.ptb-correct{border-color:var(--green);background:var(--green-bg);color:var(--green)}.ptb-dot.ptb-retry{border-color:var(--amber);background:var(--amber);color:#fff}.ptb-dot.ptb-wrong{color:#b0907a;background:#f5ebe0;border-color:#d4b8a0}.ptb-dot.ptb-pending{opacity:.6}.mc-list{flex-direction:column;gap:.6rem;width:100%;max-width:480px;margin:0 auto;display:flex}.mc-option{text-align:left;border:2px solid var(--border);background:var(--card);width:100%;font-family:var(--body);color:var(--ink);cursor:pointer;border-radius:12px;align-items:center;gap:.75rem;padding:.7rem 1rem;font-size:1rem;transition:border-color .15s,background .15s,transform .1s;display:flex}.mc-option:hover:not(:disabled){border-color:var(--blue);transform:translateY(-1px)}.mc-option:disabled{cursor:default}.mc-letter{background:var(--bg);border:2px solid var(--border);width:30px;height:30px;font-family:var(--heading);color:var(--ink2);border-radius:50%;flex-shrink:0;justify-content:center;align-items:center;font-size:.9rem;display:inline-flex}.mc-text{flex:1;line-height:1.35}.mc-mark{flex-shrink:0;font-size:1.2rem;font-weight:900}.mc-mark-ok{color:var(--green)}.mc-mark-no{color:var(--red)}.mc-selected{border-color:var(--blue);background:var(--blue-bg)}.mc-selected .mc-letter{border-color:var(--blue);color:var(--blue);background:#fff}.mc-correct{border-color:var(--green);background:var(--green-bg)}.mc-correct .mc-letter{border-color:var(--green);color:var(--green);background:#fff}.mc-incorrect{border-color:var(--red);background:#fdeceb}.mc-incorrect .mc-letter{border-color:var(--red);color:var(--red);background:#fff}.gab-wrap{margin-bottom:.8rem}.gab-button{box-sizing:border-box;color:#3c4043;border:1.5px solid var(--border);width:100%;font-family:var(--body);cursor:pointer;background:#fff;border-radius:8px;justify-content:center;align-items:center;gap:.6rem;padding:.6rem .8rem;font-size:.92rem;font-weight:700;transition:all .15s;display:flex}.gab-button:hover:not(:disabled){transform:translateY(-1px);box-shadow:0 2px 8px #0000001f}.gab-button:disabled{opacity:.6;cursor:default}.gab-icon{flex-shrink:0;width:18px;height:18px}.gab-error{color:var(--red);margin-top:.5rem;font-size:.85rem}.gab-divider{color:var(--ink2);align-items:center;gap:.7rem;margin:.9rem 0;font-size:.8rem;display:flex}.gab-divider:before,.gab-divider:after{content:"";background:var(--border);flex:1;height:1px}.sim-overlay{z-index:1000;background:#1a1a2e8c;justify-content:center;align-items:center;padding:1rem;display:flex;position:fixed;inset:0}.sim-card{background:var(--card);border:2px solid var(--border);border-radius:14px;width:100%;max-width:380px;padding:1.5rem 1.6rem;position:relative}.sim-close{cursor:pointer;color:var(--ink2);background:0 0;border:none;font-size:1.5rem;line-height:1;position:absolute;top:.6rem;right:.8rem}.sim-title{font-family:var(--heading);color:var(--ink);margin:0 0 .6rem;font-size:1.25rem}.sim-desc{color:var(--ink2);margin-bottom:1rem;font-size:.9rem;line-height:1.55}.sim-input{box-sizing:border-box;border:1.5px solid var(--border);width:100%;font-family:var(--body);color:var(--ink);background:#fff;border-radius:8px;margin-bottom:.8rem;padding:.6rem .8rem;font-size:.95rem}.sim-error{color:var(--red);margin-bottom:.7rem;font-size:.85rem}.sim-sent{background:var(--green-bg);border-left:3px solid var(--green);color:#1b5e20;border-radius:8px;padding:.8rem 1rem;font-size:.9rem;line-height:1.55}.sim-code-prompt{color:var(--ink2);margin:1rem 0 .6rem;font-size:.85rem}.sim-label{color:var(--ink2);margin-bottom:.4rem;font-size:.85rem;display:block}.sim-note{color:var(--ink2);text-align:center;margin-top:.9rem;font-size:.8rem;line-height:1.5}.sim-switch{color:var(--ink2);text-align:center;margin-top:.9rem;font-size:.85rem}.sim-switch-link{color:var(--blue);cursor:pointer;font-size:.85rem;font-weight:700;font-family:var(--body);background:0 0;border:none;padding:0;text-decoration:underline}.sim-switch-link:hover{opacity:.8}.signed-in-toast{background:var(--green-bg);border-bottom:2px solid var(--green);color:var(--green);text-align:center;padding:.65rem 1.5rem;font-size:.95rem;font-weight:700}.welcome-banner{background:var(--green-bg);border-bottom:2px solid var(--green);text-align:center;padding:1.25rem 2rem}.welcome-banner-inner{max-width:640px;margin:0 auto}.welcome-banner-title{font-family:var(--heading);color:var(--ink);margin-bottom:.4rem;font-size:1.6rem}.welcome-banner-text{color:var(--ink2);margin-bottom:1rem;font-size:1.05rem}.welcome-banner-actions{flex-wrap:wrap;justify-content:center;align-items:center;gap:1rem;display:flex}.welcome-banner-dismiss{color:var(--ink2);cursor:pointer;background:0 0;border:none;font-size:.95rem;text-decoration:underline}.site-header{padding:calc(.75rem + env(safe-area-inset-top,0px)) 2rem .75rem;background:var(--card);border-bottom:2px solid var(--border);justify-content:space-between;align-items:center;width:100%;display:flex}.site-brand{font-family:var(--heading);letter-spacing:.01em;flex-shrink:0;font-size:1.55rem;font-weight:800}.brand-link{align-items:center;gap:.4rem;display:flex}.brand-logo{object-fit:contain;width:32px;height:32px;display:block}.brand-simply{color:var(--ink)}.brand-lesson{color:var(--blue)}.site-nav{flex:1;justify-content:center;align-items:center;gap:.5rem;display:flex;position:relative}.nav-link{color:var(--ink2);border-radius:6px;padding:.3rem .6rem;font-size:.95rem;font-weight:700;text-decoration:none;transition:all .15s}.nav-link:hover{color:var(--blue);background:var(--blue-bg)}.nav-separator{color:var(--border);font-size:.9rem}.header-spacer{flex-shrink:0;width:100px}.header-account{flex-shrink:0;justify-content:flex-end;align-items:center;gap:.5rem;min-width:100px;display:flex}.account-signin{background:var(--blue);color:#fff;cursor:pointer;font-size:.85rem;font-weight:700;font-family:var(--body);border:none;border-radius:7px;padding:.4rem .85rem}.account-signin:hover{opacity:.9}.account-signup{color:var(--blue);border:1.5px solid var(--blue);cursor:pointer;font-size:.85rem;font-weight:700;font-family:var(--body);background:0 0;border-radius:7px;padding:.4rem .85rem}.account-signup:hover{background:var(--blue-bg)}.account-email{color:var(--ink2);text-overflow:ellipsis;white-space:nowrap;max-width:140px;font-size:.8rem;font-weight:700;overflow:hidden}.account-signout{border:1.5px solid var(--border);cursor:pointer;color:var(--ink2);font-size:.78rem;font-weight:700;font-family:var(--body);background:0 0;border-radius:7px;padding:.3rem .6rem}.account-signout:hover{border-color:var(--red);color:var(--red)}.nav-item-with-dropdown{position:relative}.nav-dropdown{background:var(--card);border:2px solid var(--border);z-index:1000;opacity:0;background-clip:padding-box;border-radius:8px;min-width:180px;padding-top:.5rem;animation:.2s forwards dropdownFadeIn;position:absolute;top:100%;left:0;transform:translateY(-8px);box-shadow:0 4px 12px #00000026}@keyframes dropdownFadeIn{to{opacity:1;transform:translateY(0)}}.dropdown-item{color:var(--ink);border-bottom:1px solid var(--border);justify-content:space-between;align-items:center;padding:.65rem 1rem;font-size:.9rem;font-weight:700;text-decoration:none;transition:all .15s;display:flex}.dropdown-item:last-child{border-bottom:none}.dropdown-item:hover:not(.disabled){background:var(--blue-bg);color:var(--blue)}.dropdown-item.disabled{color:var(--ink2);opacity:.6;cursor:not-allowed;pointer-events:none}.coming-soon{color:var(--amber);text-transform:uppercase;letter-spacing:.02em;background:#fff8e1;border-radius:4px;padding:.2rem .5rem;font-size:.7rem;font-weight:800}.hamburger-btn{cursor:pointer;background:0 0;border:none;flex-direction:column;flex-shrink:0;justify-content:center;align-items:center;gap:5px;width:40px;height:40px;padding:0;display:none}.hamburger-btn span{background:var(--ink);border-radius:2px;width:24px;height:3px;display:block}.mobile-menu-overlay{background:var(--bg);z-index:2000;flex-direction:column;display:flex;position:fixed;inset:0}.mobile-menu-header{padding:calc(.75rem + env(safe-area-inset-top,0px)) 2rem .75rem;background:var(--card);border-bottom:2px solid var(--border);flex-shrink:0;justify-content:space-between;align-items:center;display:flex}.mobile-menu-close{color:var(--ink);cursor:pointer;background:0 0;border:none;padding:0 .5rem;font-size:2rem;line-height:1}.mobile-menu-body{flex-direction:column;flex:1;gap:.25rem;min-height:0;padding:1rem 1.25rem;display:flex;overflow-y:auto}.mobile-nav-item{border-bottom:1px solid var(--border)}.mobile-nav-link{color:var(--ink);padding:1rem .25rem;font-size:1.1rem;font-weight:700;text-decoration:none;display:block}.mobile-nav-accordion-trigger{width:100%;color:var(--ink);cursor:pointer;font-size:1.1rem;font-weight:700;font-family:var(--body);background:0 0;border:none;justify-content:space-between;align-items:center;padding:1rem .25rem;display:flex}.mobile-accordion-arrow{color:var(--ink2);transition:transform .2s}.mobile-accordion-arrow.open{transform:rotate(180deg)}.mobile-accordion-panel{padding-bottom:.5rem}.mobile-dropdown-item{color:var(--ink);justify-content:space-between;align-items:center;padding:.65rem .25rem .65rem 1.25rem;font-size:.95rem;font-weight:700;text-decoration:none;display:flex}.mobile-dropdown-item.disabled{color:var(--ink2);opacity:.6;pointer-events:none}.mobile-menu-account{padding:1.25rem 1.25rem calc(1.25rem + env(safe-area-inset-bottom,0px));border-top:2px solid var(--border);background:var(--card);flex-direction:column;flex-shrink:0;gap:.75rem;display:flex}.mobile-menu-account .account-signin,.mobile-menu-account .account-signup,.mobile-menu-account .account-signout{width:100%;padding:.75rem;font-size:1rem}.mobile-menu-account .account-email{text-align:center;max-width:none}@media (width<=960px){.site-header{flex-wrap:nowrap}.header-spacer{display:none}.hamburger-btn{display:flex}.site-nav,.header-account{display:none}}.app-footer{text-align:center;padding:1.5rem 2rem calc(1.5rem + env(safe-area-inset-bottom,0px));color:var(--ink2);background:var(--card);width:100%;font-size:.9rem;font-family:var(--body);border-radius:0;flex-shrink:0;margin:auto 0 0}.app-footer p{margin:.5rem 0;font-weight:600}.app-footer a{color:var(--blue);font-weight:600;text-decoration:none}.app-footer a:hover{text-decoration:underline}.footer-note{opacity:.7;margin-top:1rem;font-size:.8rem;font-weight:600}