/* =================================================================
   PROFESSIONAL BASIC CALCULATOR - CYBER-NOIR THEME
================================================================= */
:root {
    --primary-glow-color: #00aeff;
    --background-dark: #0f0c29;
    --background-gradient: linear-gradient(to right, #24243e, #302b63, #0f0c29);
    --surface-color: rgba(15, 12, 41, 0.6);
    --border-color: rgba(0, 174, 255, 0.5);
}
html {
    font-size: 16px;
    box-sizing: border-box;
}
*, *:before, *:after {
    box-sizing: inherit;
}
body {
    margin: 0;
    min-height: 100vh;
    justify-content: center;
    background: var(--background-dark);
    background: -webkit-linear-gradient(to right, #24243e, #302b63, #0f0c29);
    background: var(--background-gradient);
    font-family: 'Orbitron', sans-serif;
    color: #fff;
}
.calculator-container {
    width: 100%;
    max-width: 500px;
    padding: 2rem;
    margin-top: 21%;
}
h1 {
    text-align: center;
    font-weight: 700;
    font-size: 2.5rem;
    text-shadow: 0 0 5px #fff, 0 0 10px var(--primary-glow-color);
    margin-bottom: 2rem;
}
.card {
    background: var(--surface-color);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    box-shadow: 0 0 30px rgba(0, 174, 255, 0.25);
    border-radius: 15px;
    padding: 2rem;
}
.form-group {
    margin-bottom: 1.5rem;
}
label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--primary-glow-color);
}
input[type="number"], input[type="text"] {
    width: 100%;
    padding: 0.75rem 1rem;
    background-color: rgba(0,0,0,0.3);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    color: #fff;
    font-family: inherit;
    font-size: 1.2rem;
    box-shadow: inset 0 0 10px rgba(0,0,0,0.4);
}
input#result {
    font-weight: bold;
    color: var(--primary-glow-color);
}
.button-group {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1rem;
    margin: 2rem 0;
}
.btn {
    padding: 0.75rem;
    font-family: inherit;
    font-weight: 600;
    font-size: 1.2rem;
    border-radius: 8px;
    cursor: pointer;
    text-align: center;
    transition: all 0.3s ease;
    border: 2px solid var(--primary-glow-color);
    background-color: transparent;
    color: var(--primary-glow-color);
}
.btn:hover {
    background-color: var(--primary-glow-color);
    color: var(--background-dark);
    box-shadow: 0 0 15px var(--primary-glow-color);
}