* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', sans-serif;
}

body {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: #0a0a0a;
    overflow: hidden;
}

/* animated neon background */
.bg {
    position: absolute;
    width: 100%;
    height: 100%;
    background: radial-gradient(circle at 20% 20%, #01898e33, transparent),
                radial-gradient(circle at 80% 80%, #d001d033, transparent),
                radial-gradient(circle at 50% 50%, #07f5d133, transparent);
    filter: blur(40px);
    z-index: -1;
}

.calculator {
    width: 360px;
    padding: 20px;
    border-radius: 20px;
    background: rgba(250, 3, 3, 0.05);
    backdrop-filter: blur(15px);
    box-shadow: 0 0 25px rgba(137, 247, 247, 0.2);
    border: 1px solid rgba(255,255,255,0.1);
    color: white;
    text-align: center;
}

h1 {
    margin-bottom: 15px;
    font-size: 20px;
    letter-spacing: 2px;
    color: #00f5ff;
}

.input {
    width: 100%;
    height: 70px;
    border: none;
    outline: none;
    border-radius: 12px;
    text-align: right;
    font-size: 28px;
    padding: 10px;
    color: #00f5ff;
    background: rgba(0,0,0,0.4);
    box-shadow: inset 0 0 10px rgba(134, 252, 246, 0.2);
    margin-bottom: 10px;
}

.history-controls {
    display: flex;
    justify-content: space-between;
    margin-bottom: 10px;
}

.btn {
    padding: 12px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background: rgba(255,255,255,0.08);
    color: white;
    font-size: 16px;
    transition: 0.2s;
}

.btn:hover {
    transform: scale(1.05);
    box-shadow: 0 0 10px #00f5ff;
}

.danger {
    background: rgba(255, 0, 80, 0.2);
}

.op {
    color: #fe79fe;
    font-size: 20px
}

.equal {
    grid-column: span 4;
    padding: 15px;
    background: linear-gradient(90deg, #00f5ff, #ff00ff);
    border-radius: 12px;
    font-size: 22px;
    cursor: pointer;
    border: none;
    color: black;
    font-weight: bold;
    transition: 0.3s;
}

.equal:hover {
    transform: scale(1.03);
    box-shadow: 0 0 10px #00f5ff;
}

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

.history {
    display: none;
    max-height: 100px;
    overflow-y: auto;
    margin-bottom: 10px;
    text-align: left;
}

.history-list {
    opacity: 0.9;
    font-size: 12px;
    list-style-type: disc;  
    padding-left: 20px;    
    margin: 0;
    text-align: left;
    color: #00f5ff;         
}

.history-list li {
    margin-bottom: 6px;
    font-size: 13px;
    opacity: 0.9;
}

@media (min-width: 0px) and (max-width: 480px) {

    .calculator {
        width: 80%;
        padding: 15px;
        border-radius: 15px;
    }

    h1 {
        font-size: 16px;
    }

    .input {
        height: 60px;
        font-size: 22px;
        padding: 8px;
    }

    .grid {
        gap: 8px;
    }

    .btn {
        padding: 10px;
        font-size: 14px;
        border-radius: 8px;
    }

    .equal {
        font-size: 18px;
        padding: 12px;
    }

    .history-controls {
        flex-direction: column;
        gap: 8px;
    }

    .btn.small {
        width: 100%;
    }
}