/* --- 1. GLOBAL ENVIRONMENT MATCH --- */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    /* Neon Green to Dark Green background gradient from homepage */
    background: linear-gradient(135deg, #0b2512 0%, #020c04 100%);
    color: #e2e8f0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    padding: 20px;
}

/* --- 2. CALCULATOR WINDOW CONTAINER --- */
.calculator {
    text-align: center;
    padding: 2rem;
    border: 1px solid #10b981;
    border-radius: 12px;
    background-color: rgba(10, 25, 14, 0.85);
    /* Neon glow effect matching your homepage container */
    box-shadow: 0 8px 32px 0 rgba(16, 185, 129, 0.15);
    backdrop-filter: blur(6px);
    width: 100%;
    max-width: 360px; /* Optimized structural calculator width */
}

/* --- 3. THE DISPLAY PANEL --- */
.display {
    width: 100%;
    height: 60px;
    background: rgba(2, 12, 4, 0.7);
    border: 1px solid rgba(16, 185, 129, 0.4);
    border-radius: 6px;
    padding: 0 1rem;
    color: #39ff14; /* Cyber green numeric text */
    font-size: 1.8rem;
    text-align: right;
    outline: none;
    margin-bottom: 1.5rem;
    letter-spacing: 1px;
    font-family: monospace; /* Preserves alignment for numeric evaluation strings */
    text-shadow: 0 0 5px rgba(57, 255, 20, 0.3);
    transition: all 0.3s ease;
}

/* Accent flash if the panel gains focus natively */
.display:focus {
    border-color: #39ff14;
    box-shadow: 0 0 10px rgba(57, 255, 20, 0.2);
}

/* --- 4. THE INTERACTIVE GRID SYSTEM --- */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

/* --- 5. COMPONENT ELEMENT BUTTONS --- */
.btn {
    background: rgba(16, 185, 129, 0.05);
    color: #cbd5e1; /* Base platinum grey from homepage paragraph styles */
    border: 1px solid rgba(16, 185, 129, 0.3);
    padding: 1rem 0;
    font-size: 1.1rem;
    font-weight: bold;
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.2s ease;
}

/* Shared Hover Micro-interaction */
.btn:hover {
    background: rgba(16, 185, 129, 0.2);
    border-color: #10b981;
    color: #39ff14;
    box-shadow: 0 0 10px rgba(16, 185, 129, 0.3);
    transform: translateY(-1px);
}

.btn:active {
    transform: translateY(1px);
}

/* Type Grouping A: Operator Functions (+, -, ×, ÷, sin, cos) */
.btn.operator {
    color: #10b981; /* Medium Emerald highlight */
    background: rgba(16, 185, 129, 0.1);
    border-color: rgba(16, 185, 129, 0.4);
}

.btn.operator:hover {
    color: #39ff14;
    background: rgba(16, 185, 129, 0.3);
}

/* Type Grouping B: Memory / Deletion Controls (C, DEL.) */
.btn.control {
    color: #ef4444; /* Distinct red warning tint */
    border-color: rgba(239, 68, 68, 0.3);
    background: rgba(239, 68, 68, 0.05);
}

.btn.control:hover {
    background: rgba(239, 68, 68, 0.2);
    border-color: #ef4444;
    color: #ff6b6b;
    box-shadow: 0 0 10px rgba(239, 68, 68, 0.3);
}

/* Type Grouping C: Submission/Execution (✓ / Equals Button) */
.btn.equals {
    background: #10b981;
    color: #020c04; /* High-contrast inversion matching homepage designs */
    border-color: #39ff14;
    font-size: 1.3rem;
}

.btn.equals:hover {
    background: #39ff14;
    color: #020c04;
    box-shadow: 0 0 15px rgba(57, 255, 20, 0.6);
}

/* Grid Layout Overrides (Wide '0' span matching template requirements) */
.btn.wide {
    grid-column: span 2;
}