* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'VT323', 'Courier New', monospace;
}

@import url('https://fonts.googleapis.com/css2?family=VT323&display=swap');

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: #000;
    padding: 20px;
    position: relative;
    overflow: hidden;
}

body::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: repeating-linear-gradient(
        0deg,
        rgba(0, 0, 0, 0.15),
        rgba(0, 0, 0, 0.15) 1px,
        transparent 1px,
        transparent 2px
    );
    pointer-events: none;
    z-index: 1;
}

.back-button {
    text-decoration: none;
    padding: 8px 16px;
    background: #00ff00;
    color: #000;
    font-weight: bold;
    border: 2px solid #00ff00;
    box-shadow: 4px 4px 0 #008800;
    margin-bottom: 20px;
    font-size: 1.2rem;
    text-transform: uppercase;
    position: relative;
    z-index: 2;
    text-shadow: 2px 2px #008800;
}

.back-button:hover {
    background: #00dd00;
    transform: translate(2px, 2px);
    box-shadow: 2px 2px 0 #008800;
}

.calculator {
    padding: 25px;
    border: 4px solid #00ff00;
    background: #000;
    box-shadow: 0 0 20px #00ff00;
    position: relative;
    z-index: 2;
}

.display {
    padding: 20px;
    margin-bottom: 20px;
    border: 2px solid #00ff00;
    background: #001100;
    text-align: right;
    min-height: 100px;
    position: relative;
    overflow: hidden;
}

.display::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(
        transparent 50%,
        rgba(0, 255, 0, 0.1) 50%
    );
    background-size: 100% 4px;
    pointer-events: none;
}

.previous-operand {
    font-size: 1.2rem;
    color: #00aa00;
    min-height: 24px;
    text-shadow: 0 0 5px #00ff00;
}

.current-operand {
    font-size: 2.5rem;
    color: #00ff00;
    margin-top: 10px;
    text-shadow: 0 0 10px #00ff00;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

button {
    padding: 20px;
    font-size: 1.5rem;
    border: 2px solid #00ff00;
    background: #001100;
    cursor: pointer;
    color: #00ff00;
    text-shadow: 0 0 5px #00ff00;
    transition: all 0.1s;
    font-family: 'VT323', 'Courier New', monospace;
}

button:hover {
    background: #002200;
    box-shadow: 0 0 10px #00ff00;
}

button:active {
    transform: scale(0.95);
    box-shadow: 0 0 5px #00ff00;
}

button[data-operation] {
    background: #002200;
}

button[data-equals] {
    background: #004400;
    grid-column: span 2;
}

button[data-all-clear],
button[data-delete] {
    background: #440000;
    color: #ff0000;
    border-color: #ff0000;
    text-shadow: 0 0 5px #ff0000;
}

button[data-all-clear]:hover,
button[data-delete]:hover {
    box-shadow: 0 0 10px #ff0000;
}