body {
    font-family: "Poppins", sans-serif;
    background: #f0f2f5;
    display: flex;
    justify-content: center;
    padding: 2rem;
}

.container {
    background: #fff;
    border-radius: 20px;
    padding: 2rem;
    width: 100%;
    max-width: 420px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
}

h1,
h2,
h3 {
    text-align: center;
    margin-bottom: 1rem;
    color: #333;
}

.result {
    height: 40px;
    padding: 15px;
    border-radius: 20px;
    border-color: black;
    border-width: 3px;
    border-style: solid;
}

input {
    display: flex;
    width: 93%;
    gap: 1rem;
    margin-bottom: 1rem;
}

input[type="number"] {
    flex: 1;
    padding: 0.75rem;
    font-size: 1.2rem;
    border: 2px solid #ddd;
    border-radius: 10px;
    outline: none;
    transition: border-color 0.3s;
}

.operations,
.memory-buttons,
.history-actions {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 0.75rem;
    margin-bottom: 1rem;
    margin-top: 2rem;
}

button {
    font-family: "Poppins";
    width: 60px;
    height: 60px;
    font-size: 1.4rem;
    font-weight: bold;
    background: linear-gradient(145deg, #e6e6e6, #ffffff);
    border: 2px solid #ccc;
    border-radius: 50%;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
    cursor: pointer;
    transition: all 0.2s ease;
    color: #333;
}

button:hover:not(:disabled) {
    background: #007bff;
    color: white;
    border-color: #007bff;
    transform: scale(1.05);
}

button:disabled {
    background: #f0f0f0;
    color: #aaa;
    border-color: #ddd;
    cursor: not-allowed;
}

.memory-buttons button,
.history-actions button {
    width: auto;
    height: 45px;
    padding: 0 1rem;
    font-size: 1rem;
    border-radius: 12px;
}

#result {
    text-align: center;
    font-size: 1.5rem;
    font-weight: bold;
    margin: 1rem 0;
    color: #222;
}

#historyList {
    padding-left: 1.5rem;
    color: #444;
}