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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: #d3d3d3;
    overflow: hidden;
    transition: background 0.3s;
}

body.dark {
    background: #1a1a1a;
}

.toggle-btn {
    position: fixed;
    top: 18px;
    right: 18px;
    background: #444;
    color: white;
    border: none;
    padding: 7px 14px;
    border-radius: 20px;
    font-size: 14px;
    cursor: pointer;
}

body.dark .toggle-btn {
    background: #ddd;
    color: #222;
}

.main {
    width: 340px;
    background: navajowhite;
    border: 2px solid black;
    border-radius: 6px;
    overflow: hidden;
    transition: background 0.3s;
}

body.dark .main {
    background: #2b2b2b;
    border-color: #555;
}

.answerbox {
    height: 90px;
    background: black;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: flex-end;
    padding: 10px 15px;
}

.expr {
    color: #888;
    font-size: 13px;
    min-height: 16px;
    font-family: monospace;
}

.answer {
    color: white;
    font-size: 32px;
    font-family: monospace;
}

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

.input {
    border: 1px solid black;
    padding: 22px;
    font-size: 20px;
    text-align: center;
    background: #f2f2f2;
    cursor: pointer;
    transition: background 0.15s;
}

body.dark .input {
    background: #3a3a3a;
    color: #f0f0f0;
    border-color: #555;
}

.input:hover  { background: #e0e0e0; }
.input:active { background: #c8c8c8; }

body.dark .input:hover  { background: #4a4a4a; }
body.dark .input:active { background: #555; }

#AC    { grid-column: 1 / 3; background: #ffe0e0; }
#equal { grid-column: 3 / 5; background: #d4edda; }

body.dark #AC    { background: #5c2a2a; color: #ffaaaa; }
body.dark #equal { background: #1e4d2b; color: #aaffbb; }

#AC:hover    { background: #ffc8c8; }
#equal:hover { background: #b8dfc4; }

body.dark #AC:hover    { background: #6e3333; }
body.dark #equal:hover { background: #255c35; }

#divide, #multiply, #plus, #minus {
    color: #5533aa;
    font-weight: bold;
}

body.dark #divide,
body.dark #multiply,
body.dark #plus,
body.dark #minus {
    color: #bb99ff;
}