Barbell Calculator in Javascript

  <div class="calculator-container">
        <div class="header">
            <h1>Barbell Calculator</h1>
            <p>Calculate plates needed for your target weight</p>
        </div>

        <div class="input-group">
            <label for="targetWeight">Target Weight</label>
            <div class="input-wrapper">
                <input type="number" id="targetWeight" placeholder="Enter weight" min="0" step="0.5">
                <span class="unit" id="weightUnit">kg</span>
            </div>
            <div class="unit-toggle">
                <button class="unit-btn active" data-unit="kg">Kilograms (kg)</button>
                <button class="unit-btn" data-unit="lbs">Pounds (lbs)</button>
            </div>
        </div>

        <div class="input-group">
            <label for="barWeight">Barbell Weight</label>
            <div class="input-wrapper">
                <input type="number" id="barWeight" value="20" min="0" step="0.5">
                <span class="unit" id="barUnit">kg</span>
            </div>
        </div>

        <button class="calculate-btn" id="calculateBtn">Calculate Plates</button>

        <div class="result" id="result">
            <div class="result-title">Plates Needed (per side):</div>
            <div class="plate-list" id="plateList"></div>
            <div class="barbell-visual">
                <div class="barbell-bar"></div>
            </div>
            <div class="note" id="totalWeight"></div>
        </div>
  </div>

   * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background: linear-gradient(135deg, #6a040f 0%, #3d0208 100%);
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 20px;
        }

        .calculator-container {
            background: white;
            border-radius: 20px;
            box-shadow: 0 10px 40px rgba(0, 0, 0, 0.3);
            max-width: 500px;
            width: 100%;
            padding: 40px;
        }

        .header {
            text-align: center;
            margin-bottom: 30px;
        }

        .header h1 {
            color: #6a040f;
            font-size: 2rem;
            font-weight: 600;
            margin-bottom: 10px;
        }

        .header p {
            color: #666;
            font-size: 0.95rem;
        }

        .input-group {
            margin-bottom: 25px;
        }

        .input-group label {
            display: block;
            color: #333;
            font-weight: 500;
            margin-bottom: 8px;
            font-size: 0.95rem;
        }

        .input-wrapper {
            position: relative;
            display: flex;
            align-items: center;
        }

        input[type="number"] {
            width: 100%;
            padding: 15px;
            border: 2px solid #e0e0e0;
            border-radius: 10px;
            font-size: 1.1rem;
            transition: all 0.3s ease;
            outline: none;
        }

        input[type="number"]:focus {
            border-color: #6a040f;
            box-shadow: 0 0 0 3px rgba(106, 4, 15, 0.1);
        }

        .unit {
            position: absolute;
            right: 15px;
            color: #6a040f;
            font-weight: 600;
            font-size: 0.9rem;
        }

        .unit-toggle {
            display: flex;
            gap: 10px;
            margin-top: 10px;
        }

        .unit-btn {
            flex: 1;
            padding: 10px;
            border: 2px solid #e0e0e0;
            background: white;
            border-radius: 8px;
            cursor: pointer;
            transition: all 0.3s ease;
            font-weight: 500;
            color: #666;
        }

        .unit-btn.active {
            background: #6a040f;
            color: white;
            border-color: #6a040f;
        }

        .calculate-btn {
            width: 100%;
            padding: 18px;
            background: linear-gradient(135deg, #6a040f 0%, #3d0208 100%);
            color: white;
            border: none;
            border-radius: 10px;
            font-size: 1.1rem;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            margin-top: 10px;
        }

        .calculate-btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 8px 20px rgba(106, 4, 15, 0.3);
        }

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

        .result {
            margin-top: 30px;
            padding: 25px;
            background: linear-gradient(135deg, #fff5f5 0%, #ffe5e5 100%);
            border-radius: 15px;
            border-left: 5px solid #6a040f;
            display: none;
        }

        .result.show {
            display: block;
            animation: slideIn 0.4s ease;
        }

        @keyframes slideIn {
            from {
                opacity: 0;
                transform: translateY(-10px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        .result-title {
            color: #6a040f;
            font-weight: 600;
            margin-bottom: 15px;
            font-size: 1.1rem;
        }

        .plate-list {
            display: flex;
            flex-direction: column;
            gap: 12px;
        }

        .plate-item {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 12px 15px;
            background: white;
            border-radius: 8px;
            box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
        }

        .plate-weight {
            font-weight: 600;
            color: #6a040f;
            font-size: 1rem;
        }

        .plate-count {
            color: #666;
            font-size: 0.9rem;
        }

        .barbell-visual {
            margin-top: 20px;
            text-align: center;
            padding: 20px;
            background: white;
            border-radius: 10px;
        }

        .barbell-bar {
            height: 12px;
            background: #6a040f;
            margin: 10px auto;
            border-radius: 6px;
            width: 80%;
            position: relative;
        }

        .note {
            margin-top: 15px;
            padding: 15px;
            background: rgba(106, 4, 15, 0.05);
            border-radius: 8px;
            font-size: 0.85rem;
            color: #666;
            text-align: center;
        }

        @media (max-width: 600px) {
            .calculator-container {
                padding: 25px;
            }

            .header h1 {
                font-size: 1.6rem;
            }
        }

  let currentUnit = 'kg';
        const unitBtns = document.querySelectorAll('.unit-btn');
        const weightUnit = document.getElementById('weightUnit');
        const barUnit = document.getElementById('barUnit');
        const targetWeight = document.getElementById('targetWeight');
        const barWeight = document.getElementById('barWeight');
        const calculateBtn = document.getElementById('calculateBtn');
        const result = document.getElementById('result');
        const plateList = document.getElementById('plateList');
        const totalWeight = document.getElementById('totalWeight');

        // Available plates
        const platesKg = [25, 20, 15, 10, 5, 2.5, 1.25, 0.5];
        const platesLbs = [45, 35, 25, 10, 5, 2.5];

        // Unit toggle
        unitBtns.forEach(btn => {
            btn.addEventListener('click', () => {
                unitBtns.forEach(b => b.classList.remove('active'));
                btn.classList.add('active');
                currentUnit = btn.dataset.unit;
                weightUnit.textContent = currentUnit;
                barUnit.textContent = currentUnit;
                
                // Update bar weight default
                if (currentUnit === 'kg') {
                    barWeight.value = '20';
                } else {
                    barWeight.value = '45';
                }
            });
        });

        // Calculate plates
        calculateBtn.addEventListener('click', () => {
            const target = parseFloat(targetWeight.value);
            const bar = parseFloat(barWeight.value);

            if (!target || target <= 0) {
                alert('Please enter a valid target weight');
                return;
            }

            if (target <= bar) {
                alert('Target weight must be greater than barbell weight');
                return;
            }

            const weightPerSide = (target - bar) / 2;
            const plates = currentUnit === 'kg' ? platesKg : platesLbs;
            const plateCount = calculatePlates(weightPerSide, plates);

            displayResult(plateCount, target, currentUnit);
        });

        function calculatePlates(weight, availablePlates) {
            const plates = {};
            let remaining = weight;

            for (const plate of availablePlates) {
                const count = Math.floor(remaining / plate);
                if (count > 0) {
                    plates[plate] = count;
                    remaining -= count * plate;
                }
            }

            return plates;
        }

        function displayResult(plates, total, unit) {
            plateList.innerHTML = '';
            
            if (Object.keys(plates).length === 0) {
                plateList.innerHTML = '<div class="plate-item"><span>No plates needed</span></div>';
            } else {
                for (const [weight, count] of Object.entries(plates)) {
                    const item = document.createElement('div');
                    item.className = 'plate-item';
                    item.innerHTML = `
                        <span class="plate-weight">${weight} ${unit}</span>
                        <span class="plate-count">× ${count} plate${count > 1 ? 's' : ''}</span>
                    `;
                    plateList.appendChild(item);
                }
            }

            totalWeight.textContent = `Total weight: ${total} ${unit}`;
            result.classList.add('show');
        }