*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
    background: radial-gradient(1200px 600px at 10% 10%, rgba(255,255,255,0.06), transparent),
                radial-gradient(1000px 500px at 90% 20%, rgba(255,255,255,0.04), transparent),
                linear-gradient(135deg, #0a0b10, #151722 60%, #1b1e2a);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 32px;
}

.container {
    width: 100%;
    max-width: 460px;
    background-color: #111217;
    color: #e9ecf1;
    border: 1px solid #23242b;
    border-radius: 18px;
    padding: 20px;
    box-shadow: 0 20px 60px rgba(0,0,0,0.5);
}

.header {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 14px;
}
.title {
    font-size: 18px;
    color: #cbd2e1;
    letter-spacing: 0.4px;
}
.logo { width: 28px; height: 28px; display: grid; place-items: center; }

.display {
    background-color: #1a1b21;
    border: 1px solid #2a2b33;
    border-radius: 14px;
    padding: 16px 18px;
    min-height: 96px;
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    justify-content: center;
    gap: 6px;
}
.expression {
    color: #99a1b3;
    min-height: 20px;
    font-size: 18px;
    word-break: break-all;
}
.result {
    font-size: 40px;
    font-weight: 700;
    color: #e9ecf1;
    word-break: break-all;
}

.grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
    margin-top: 18px;
}

.btn {
    background-color: #1e2027;
    color: #e9ecf1;
    border: 1px solid #2a2d36;
    padding: 16px 12px;
    border-radius: 14px;
    font-size: 20px;
    line-height: 1;
    cursor: pointer;
    transition: background-color 120ms ease, transform 60ms ease, border-color 120ms ease;
}
.btn:hover { background-color: #242732; }
.btn:active { transform: translateY(1px); }
.btn:focus { outline: none; }

.btn.op { color: #ffd580; }
.btn.action { color: #ff8f8f; }
.btn.primary {
    background: linear-gradient(135deg, #6a8dff, #7a58ff);
    border: none;
}

/* history styles removed */

@media (max-width: 380px) {
    .result { font-size: 32px; }
    .btn { font-size: 18px; padding: 14px 10px; }
}