*{margin:0;padding:0;box-sizing:border-box}body{font-family:Segoe UI,Tahoma,Geneva,Verdana,sans-serif;line-height:1.6;color:#333;background-color:#f5f5f5}header{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff;padding:2rem 1rem;text-align:center;box-shadow:0 2px 10px #0000001a}header h1{font-size:2.5rem;margin-bottom:.5rem;font-weight:300}header p{font-size:1.1rem;opacity:.9}nav{background:#fff;padding:0;display:flex;justify-content:center;box-shadow:0 2px 5px #0000001a;flex-wrap:wrap}.tab-button{background:none;border:none;padding:1rem 2rem;cursor:pointer;font-size:1rem;font-weight:500;color:#666;border-bottom:3px solid transparent;transition:all .3s ease}.tab-button:hover{background-color:#f0f0f0;color:#333}.tab-button.active{color:#667eea;border-bottom-color:#667eea;background-color:#f8f9ff}main{max-width:1200px;margin:0 auto;padding:2rem 1rem}.tab-content{display:none;background:#fff;border-radius:12px;padding:2rem;box-shadow:0 4px 20px #0000001a}.tab-content.active{display:block}h2{color:#333;margin-bottom:2rem;font-size:2rem;font-weight:300;border-bottom:2px solid #eee;padding-bottom:1rem}.resolution-container{padding:1rem}.resolution-display{display:grid;gap:2rem;grid-template-columns:repeat(auto-fit,minmax(300px,1fr))}.resolution-item{border:2px solid #e0e0e0;border-radius:8px;padding:1rem;text-align:center;transition:all .3s ease;background:#fafafa}.resolution-item:hover{border-color:#667eea;box-shadow:0 4px 15px #667eea33;transform:translateY(-2px)}.resolution-rect{border:2px solid #333;margin:0 auto 1rem;background:linear-gradient(45deg,#f0f0f0 25%,transparent 25%),linear-gradient(-45deg,#f0f0f0 25%,transparent 25%),linear-gradient(45deg,transparent 75%,#f0f0f0 75%),linear-gradient(-45deg,transparent 75%,#f0f0f0 75%);background-size:20px 20px;background-position:0 0,0 10px,10px -10px,-10px 0px}.resolution-info{display:flex;flex-direction:column;gap:.5rem}.resolution-label{font-size:1.3rem;font-weight:700;color:#333}.pixel-count{font-size:1.1rem;color:#667eea;font-weight:500}.device-info{font-size:.9rem;color:#888;font-style:italic}.pixel-controls{display:flex;gap:2rem;margin-bottom:2rem;flex-wrap:wrap;align-items:center}.pixel-controls label{display:flex;align-items:center;gap:.5rem;font-weight:500}.pixel-controls select,.pixel-controls input[type=range]{padding:.5rem;border:1px solid #ddd;border-radius:4px;font-size:1rem}.pixel-info-display{display:flex;gap:2rem;margin-top:1rem;font-size:.9rem;color:#666}.pixel-info-display span{background:#f8f9ff;padding:.5rem 1rem;border-radius:4px;border:1px solid #e0e0e0}.pixel-display-container{display:flex;gap:2rem;align-items:flex-start;overflow:auto;max-height:80vh}.canvas-wrapper{overflow:auto;max-width:70vw;max-height:70vh;border:2px solid #333;background:#fff;position:relative}#pixel-canvas{cursor:crosshair;background:#fff;display:block}.pixel-info-panel{background:#f8f9ff;border:1px solid #e0e0e0;border-radius:8px;padding:1.5rem;min-width:250px}.pixel-info-panel h3{margin-bottom:1rem;color:#333;font-size:1.2rem}.calculator-container{display:grid;gap:2rem;grid-template-columns:1fr 2fr 1fr}.input-section,.calculation-section,.result-section{background:#f8f9ff;border-radius:8px;padding:1.5rem}.input-section h3,.calculation-section h3,.result-section h3{margin-bottom:1rem;color:#333;font-size:1.3rem;border-bottom:1px solid #eee;padding-bottom:.5rem}.input-group{display:flex;flex-direction:column;gap:1rem}.input-group label{display:flex;flex-direction:column;gap:.5rem;font-weight:500}.input-group input,.input-group select{padding:.75rem;border:1px solid #ddd;border-radius:4px;font-size:1rem}.calculation-step{display:grid;grid-template-columns:auto 1fr auto;gap:1rem;align-items:center;padding:.75rem;margin-bottom:.5rem;border-radius:4px;background:#fff;border-left:4px solid #667eea}.step-number{font-weight:700;color:#667eea;font-size:1.1rem}.step-description{color:#555}.step-result{font-weight:700;color:#333;font-family:Courier New,monospace}.final-result{text-align:center}.result-value{display:block;font-size:3rem;font-weight:700;color:#667eea;margin-bottom:1rem}.comparison-info{background:#fff;border-radius:4px;padding:1rem;text-align:left}.comparison-info p{margin-bottom:.5rem;font-size:.9rem}.color-depth-container{padding:1rem}.sample-image-controls{margin-bottom:2rem;text-align:center}.sample-image-controls label{display:inline-flex;align-items:center;gap:.5rem;font-weight:500;font-size:1.1rem}.sample-image-controls select{padding:.5rem;border:1px solid #ddd;border-radius:4px;font-size:1rem}.color-depth-comparison{display:grid;grid-template-columns:repeat(auto-fit,minmax(250px,1fr));gap:2rem}.depth-item{text-align:center;background:#f8f9ff;border-radius:8px;padding:1.5rem;border:1px solid #e0e0e0}.depth-item canvas{border:1px solid #ccc;margin-bottom:1rem}.depth-info h4{margin-bottom:.5rem;color:#333;font-size:1.1rem}.depth-info p{color:#666;font-size:.9rem}.practice-container{padding:1rem}.level-selector{display:flex;gap:1rem;margin-bottom:2rem;justify-content:center;flex-wrap:wrap}.level-button{padding:.75rem 1.5rem;border:2px solid #667eea;background:#fff;color:#667eea;border-radius:25px;cursor:pointer;font-weight:500;transition:all .3s ease}.level-button:hover,.level-button.active{background:#667eea;color:#fff}.problem-container{background:#f8f9ff;border-radius:8px;padding:2rem;margin-bottom:2rem}.problem h3{margin-bottom:1rem;color:#333;font-size:1.5rem}.problem p{margin-bottom:2rem;font-size:1.1rem;line-height:1.6}.answer-input{display:flex;gap:1rem;margin-bottom:2rem;align-items:center;flex-wrap:wrap}.answer-input input{flex:1;min-width:200px;padding:.75rem;border:1px solid #ddd;border-radius:4px;font-size:1rem}.answer-input select{padding:.75rem;border:1px solid #ddd;border-radius:4px;font-size:1rem}.problem-buttons{display:flex;gap:1rem;flex-wrap:wrap}.problem-buttons button{padding:.75rem 1.5rem;border:none;border-radius:4px;cursor:pointer;font-size:1rem;font-weight:500;transition:all .3s ease}#hint-button{background:#ffc107;color:#333}#hint-button:hover{background:#e0a800}#check-answer{background:#28a745;color:#fff}#check-answer:hover{background:#218838}#next-problem{background:#667eea;color:#fff}#next-problem:hover{background:#5a67d8}.feedback{margin-top:1rem;padding:1rem;border-radius:4px;font-weight:500}.feedback.correct{background:#d4edda;color:#155724;border:1px solid #c3e6cb}.feedback.incorrect{background:#f8d7da;color:#721c24;border:1px solid #f5c6cb}.hint-panel{margin-top:1rem;padding:1rem;background:#e7f3ff;border:1px solid #b3d7ff;border-radius:4px;display:none}.progress-info{text-align:center;font-size:1.1rem;font-weight:500}.score{color:#667eea}.completion-status{margin-top:1rem;font-weight:700;text-align:center}.completion-status.completed{color:#28a745;font-size:1.2rem}.completion-status button{background:linear-gradient(135deg,#28a745,#20c997);color:#fff;border:none;padding:1rem 2rem;border-radius:25px;font-size:1.1rem;font-weight:700;cursor:pointer;margin-top:1rem;box-shadow:0 4px 15px #28a7454d;transition:all .3s ease}.completion-status button:hover{transform:translateY(-2px);box-shadow:0 6px 20px #28a74566}.certificate-modal{display:none;position:fixed;z-index:1000;left:0;top:0;width:100%;height:100%;background-color:#000c;-webkit-backdrop-filter:blur(5px);backdrop-filter:blur(5px)}.certificate-container{position:relative;margin:2% auto;background:#fff;border-radius:15px;box-shadow:0 10px 30px #0000004d;max-width:900px;padding:2rem;text-align:center}.certificate-close{position:absolute;top:15px;right:25px;font-size:2rem;font-weight:700;color:#999;cursor:pointer;transition:color .3s ease}.certificate-close:hover{color:#333}#certificate-canvas{border:3px solid #667eea;border-radius:10px;margin:1rem 0;box-shadow:0 4px 15px #0000001a}.certificate-buttons{display:flex;gap:1rem;justify-content:center;margin-top:1.5rem}.download-btn{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff;border:none;padding:1rem 2rem;border-radius:25px;font-size:1.1rem;font-weight:700;cursor:pointer;box-shadow:0 4px 15px #667eea4d;transition:all .3s ease}.download-btn:hover{transform:translateY(-2px);box-shadow:0 6px 20px #667eea66}.close-btn{background:#6c757d;color:#fff;border:none;padding:1rem 2rem;border-radius:25px;font-size:1.1rem;font-weight:700;cursor:pointer;transition:all .3s ease}.close-btn:hover{background:#5a6268;transform:translateY(-2px)}@media (max-width: 768px){.calculator-container{grid-template-columns:1fr}.pixel-display-container{flex-direction:column;gap:1rem}.canvas-wrapper{max-width:calc(100vw - 4rem);max-height:50vh}.pixel-controls{flex-direction:column;align-items:stretch;gap:1rem}.pixel-info-display{flex-direction:column;gap:.5rem}.color-depth-comparison{grid-template-columns:repeat(auto-fit,minmax(200px,1fr))}.tab-button{padding:.75rem 1rem;font-size:.9rem}header h1{font-size:2rem}.resolution-display{grid-template-columns:1fr}}@media (max-width: 480px){main{padding:1rem .5rem}.tab-content{padding:1rem}.tab-button{padding:.5rem .75rem;font-size:.8rem}.canvas-wrapper{max-width:calc(100vw - 3rem);max-height:40vh}.pixel-controls{gap:.75rem}.pixel-controls label{flex-direction:column;align-items:stretch;text-align:left}.pixel-controls select,.pixel-controls input[type=range]{width:100%;margin-top:.25rem}}