*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    font-family: "Zen Dots", sans-serif;
    background-color: #ffffff;
    gap: 20px;
}

#mode_toggle {
    padding: 10px 20px;
    font-family: "Zen Dots", sans-serif;
    background: #b18597;
    color: white;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    font-size: 16px;
    transition: transform 0.2s;
}
#mode_toggle:hover {
    transform: scale(1.05);
}

#calculator_body {
    display: grid;
    grid-template-columns: 1fr; 
    gap: 12px;
    width: 440px;         
    padding: 16px;       
    background: #fff0f0;
    border: 2px solid #b18597;
    border-radius: 15px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    transition: width 0.3s ease;
}

/* advanced mode */
#calculator_body.advanced {
    width: 700px;
    grid-template-columns: 1fr 1.5fr; 
}

.sci_keys {
    display: none;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
}

#calculator_body.advanced .sci_keys {
    display: grid;
}

#calculator_screen {
    grid-column: 1 / -1; 
    width: 100%;
    min-height: 64px;
    padding: 12px;
    background-color: rgb(191, 255, 255);
    border: 2px solid #b18597;
    border-radius: 10px;
    text-align: right;
    font-size: clamp(22px, 4vw, 36px);
    word-break: break-all;
}

.std_keys {
    display: flex;
    flex-direction: column;
}

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

button {
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    border: none;
    outline: none;
    font-family: inherit;
    user-select: none;
    transition: all 0.15s ease;
}

button.btn {
    font-size: clamp(14px, 2vw, 22px); 
    font-weight: 100;
    text-transform: uppercase;
    padding: 0.8em 0;
    background: #fff0f0;
    border: 2px solid #b18597;
    border-radius: 0.75em;
    position: relative;
    transform-style: preserve-3d;
}

button.btn::before {
    content: '';
    position: absolute;
    top: 0; left: 0; right: 0; bottom: 0;
    background: #f9c4d2;
    border-radius: inherit;
    box-shadow: 0 0 0 2px #b18597, 0 0.5em 0 0 #ffe3e2;
    transform: translate3d(0, 0.5em, -1em);
    transition: transform 150ms cubic-bezier(0,0,0.58,1), box-shadow 150ms cubic-bezier(0,0,0.58,1);
}

button.btn:hover { background: #ffe9e9; transform: translateY(0.25em); }
button.btn:hover::before { transform: translate3d(0, 0.35em, -1em); }
button.btn:active { background: #ffe9e9; transform: translateY(0.75em); }
button.btn:active::before { transform: translate3d(0, 0, -1em); box-shadow: 0 0 0 2px #b18597, 0 0 #ffe3e2; }

@media (max-width: 600px) {
    #calculator_body {
        width: 95%;
        max-width: 400px; 
        padding: 12px;
        gap: 8px;
    }

    #calculator_body.advanced { width: 95%; grid-template-columns: 1fr; }
    .sci_keys {
        grid-template-columns: repeat(4, 1fr); 
        gap: 8px;
        margin-bottom: 5px;
        border-bottom: 2px dashed #b18597; 
        padding-bottom: 10px;
    }
    button.btn {
        font-size: 18px;
        padding: 0.6em 0;
    }

    #calculator_screen {
        font-size: 24px;
        min-height: 50px;
    }
}