:root{--bg-primary: #ffffff;--bg-secondary: #f8f9fb;--bg-tertiary: #f0f1f4;--text-primary: #1a1a2e;--text-secondary: #555770;--text-muted: #8b8da3;--accent: #5b5fc7;--accent-hover: #4a4eb8;--accent-light: #eeeef9;--success: #2e7d57;--success-light: #e8f5e9;--error: #c62828;--error-light: #fce4ec;--warning: #e8811a;--warning-light: #fff3e0;--border: #e0e1e6;--preview-bg: #ffffff}*{margin:0;padding:0;box-sizing:border-box}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,sans-serif;background:var(--bg-primary);color:var(--text-primary);overflow:hidden;height:100vh}#app{display:flex;flex-direction:column;height:100vh}.header{display:flex;align-items:center;justify-content:space-between;padding:10px 20px;background:var(--bg-primary);border-bottom:1px solid var(--border);flex-shrink:0}.header-title{font-size:18px;font-weight:700;color:var(--accent);letter-spacing:.3px}.header-progress{font-size:13px;color:var(--text-secondary)}.header-progress .count{color:var(--success);font-weight:600}.lang-btn{padding:4px 10px;border:1px solid var(--border);border-radius:4px;background:none;color:var(--text-secondary);font-size:12px;cursor:pointer;transition:border-color .15s,color .15s}.lang-btn:hover{border-color:var(--accent);color:var(--accent)}.exercise-nav{display:flex;gap:6px;padding:8px 20px;background:var(--bg-secondary);border-bottom:1px solid var(--border);overflow-x:auto;flex-shrink:0}.exercise-nav::-webkit-scrollbar{height:3px}.exercise-nav::-webkit-scrollbar-thumb{background:var(--border);border-radius:2px}.nav-btn{padding:5px 14px;border:1px solid var(--border);border-radius:6px;background:var(--bg-primary);color:var(--text-secondary);font-size:12px;cursor:pointer;white-space:nowrap;transition:all .15s}.nav-btn:hover{background:var(--bg-tertiary);color:var(--text-primary);border-color:var(--text-muted)}.nav-btn.active{background:var(--accent);border-color:var(--accent);color:#fff}.nav-btn.completed{border-color:var(--success);color:var(--success);background:var(--success-light)}.nav-btn.completed.active{background:var(--success);border-color:var(--success);color:#fff}.nav-btn .check{margin-right:4px}.main-container{display:flex;flex:1;overflow:hidden}.left-panel{width:45%;display:flex;flex-direction:column;border-right:1px solid var(--border);background:var(--bg-primary)}.exercise-info{padding:14px 20px;border-bottom:1px solid var(--border);flex-shrink:0}.exercise-title{font-size:15px;font-weight:600;margin-bottom:6px;color:var(--text-primary)}.exercise-instructions{font-size:13px;color:var(--text-secondary);line-height:1.6;white-space:pre-wrap;max-height:120px;overflow-y:auto}.exercise-instructions code{background:var(--bg-tertiary);padding:1px 5px;border-radius:3px;font-family:Fira Code,monospace;font-size:12px;color:var(--accent)}.editor-container{flex:1;overflow:hidden;border-bottom:1px solid var(--border)}.editor-actions{display:flex;gap:8px;padding:8px 16px;flex-shrink:0;background:var(--bg-secondary)}.btn{padding:6px 16px;border:1px solid var(--border);border-radius:6px;background:var(--bg-primary);color:var(--text-secondary);font-size:12px;cursor:pointer;transition:all .15s}.btn:hover{background:var(--bg-tertiary);color:var(--text-primary);border-color:var(--text-muted)}.btn-primary{background:var(--accent);border-color:var(--accent);color:#fff}.btn-primary:hover{background:var(--accent-hover);border-color:var(--accent-hover)}.btn-hint{margin-left:auto}.right-panel{width:55%;display:flex;flex-direction:column;background:var(--bg-primary)}.preview-sections{flex:1;display:flex;flex-direction:column;overflow:hidden}.preview-section{flex:1;display:flex;flex-direction:column;border-bottom:1px solid var(--border);overflow:hidden;min-height:0}.preview-section:last-child{border-bottom:none}.preview-label{font-size:11px;font-weight:600;text-transform:uppercase;letter-spacing:.5px;color:var(--text-muted);padding:4px 12px;background:var(--bg-secondary);border-bottom:1px solid var(--border);flex-shrink:0}.preview-content{flex:1;overflow:hidden;background:#c8c8c8;padding:12px;display:flex;align-items:center;justify-content:center;min-height:0}.preview-content svg{max-width:calc(100% - 16px);max-height:calc(100% - 16px);width:auto;height:auto;box-shadow:0 2px 8px #00000047}.preview-content canvas{max-width:calc(100% - 16px);max-height:calc(100% - 16px);width:auto;height:auto;box-shadow:0 2px 8px #00000047}#diff-content{background-color:#fff;background-image:linear-gradient(45deg,#d0d0d0 25%,transparent 25%),linear-gradient(-45deg,#d0d0d0 25%,transparent 25%),linear-gradient(45deg,transparent 75%,#d0d0d0 75%),linear-gradient(-45deg,transparent 75%,#d0d0d0 75%);background-size:16px 16px;background-position:0 0,0 8px,8px -8px,-8px 0px}#diff-content canvas{box-shadow:none}.preview-error{padding:12px 16px;color:var(--error);font-family:Fira Code,monospace;font-size:12px;white-space:pre-wrap;background:var(--error-light);border-radius:4px;width:100%}.preview-placeholder{display:flex;align-items:center;justify-content:center;height:100%;width:100%;color:var(--text-muted);font-size:13px}.preview-size-mismatch{display:flex;flex-direction:column;align-items:center;justify-content:center;gap:8px;height:100%;width:100%;color:var(--warning);font-size:13px;text-align:center;padding:16px}.preview-size-mismatch .size-icon{font-size:28px}.preview-size-mismatch .size-detail{font-size:12px;color:var(--text-muted);font-family:Fira Code,monospace}.match-status{padding:8px 16px;display:flex;align-items:center;gap:12px;border-top:1px solid var(--border);background:var(--bg-secondary);flex-shrink:0}.match-bar{flex:1;height:6px;background:var(--bg-tertiary);border-radius:3px;overflow:hidden}.match-bar-fill{height:100%;border-radius:3px;transition:width .3s,background-color .3s}.match-text{font-size:13px;font-weight:600;min-width:80px;text-align:right}.match-text.perfect{color:var(--success)}.match-text.close{color:var(--warning)}.match-text.far{color:var(--error)}.hint-panel{padding:10px 16px;background:var(--warning-light);border-top:1px solid var(--border);color:var(--warning);font-size:13px;line-height:1.5;display:none;flex-shrink:0}.hint-panel.visible{display:block}.loading-overlay{position:fixed;top:0;right:0;bottom:0;left:0;background:var(--bg-primary);display:flex;flex-direction:column;align-items:center;justify-content:center;z-index:100;gap:16px}.loading-spinner{width:36px;height:36px;border:3px solid var(--border);border-top-color:var(--accent);border-radius:50%;animation:spin 1s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.loading-text{color:var(--text-secondary);font-size:14px}.preview-tab-bar{display:none}@media(max-width:768px){.main-container{flex-direction:column}.left-panel{width:100%;flex:0 0 50%;border-right:none;border-bottom:1px solid var(--border)}.right-panel{width:100%;flex:1;min-height:0}.preview-tab-bar{display:flex;flex-shrink:0;border-bottom:1px solid var(--border);background:var(--bg-secondary)}.preview-tab-btn{flex:1;padding:8px 4px;border:none;border-bottom:2px solid transparent;background:none;color:var(--text-muted);font-size:12px;font-weight:500;cursor:pointer;transition:color .15s,border-color .15s}.preview-tab-btn.active{color:var(--accent);border-bottom-color:var(--accent);background:var(--bg-primary)}.preview-section{display:none}#preview-sections[data-tab=current] #preview-current,#preview-sections[data-tab=expected] #preview-expected,#preview-sections[data-tab=diff] #preview-diff{display:flex;flex:1}.exercise-instructions{max-height:80px}}