* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: system-ui, sans-serif;
}

:root {
    /* Tema claro - Cores mais vibrantes e contrastantes */
    --bg: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    --calculator-bg: rgba(201, 201, 201, 0.9);
    --display-bg: #2d3436;
    --display-color: #ffffff;
    --btn-bg: #e9e9e9;
    --btn-color: #2d3436;
    --btn-hover: #b8b8b8;
    --equal-bg: linear-gradient(135deg, #0ab18a 0%, #04664f 100%);
    --equal-hover: #04664f;
    --clear-bg: linear-gradient(135deg, #d63031 0%, #ff6b6b 100%);
    --clear-hover: #b02222;
    --back-bg: linear-gradient(135deg, #facc15 0%, #ffd700 100%);
    --back-color: #2d3436;
    --back-hover: #e1a93f;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    --border-radius: 20px;
}

body.dark {
    /* Dark theme */
    --bg: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
    --calculator-bg: rgba(30, 30, 46, 0.95);
    --display-bg: #0f0f1a;
    --display-color: #ffffff;
    --btn-bg: rgba(255, 255, 255, 0.08);
    --btn-color: #e0e0e0;
    --btn-hover: rgba(255, 255, 255, 0.15);
    --operator-bg: rgba(33, 150, 243, 0.2);
    --operator-color: #4fc3f7;
    --equal-bg: linear-gradient(135deg, #00cec9 0%, #088b89 100%);
    --equal-hover: #00b894;
    --clear-bg: linear-gradient(135deg, #d63031 0%, #e17055 100%);
    --clear-hover: #ff5252;
    --back-bg: linear-gradient(135deg, #fdcb6e 0%, #ffeaa7 100%);
    --back-color: #2d3436;
    --back-hover: #fab43f;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.4);
}

body {
    background: var(--bg);
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

/* Change theme button */
.theme-toggle {
    position: absolute;
    top: 25px;
    right: 25px;
    padding: 12px 20px;
    border-radius: 50px;
    border: none;
    cursor: pointer;
    background: var(--btn-bg);
    color: var(--btn-color);
    backdrop-filter: blur(10px);
    font-weight: 600;
    font-size: 1rem;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
    display: flex;
    align-items: center;
    gap: 8px;
    z-index: 100;
}

.theme-toggle:hover {
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.25);
}

/* Container - calculator*/
.calculator {
    margin: 10px 0px 10px 0;
    width: 100%;
    max-width: 380px;
    max-height: 800px;
    padding: 25px;
    border-radius: var(--border-radius);
    background: var(--calculator-bg);
    box-shadow: var(--shadow);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

/* Display */
.display {
    margin-bottom: 25px;
    position: relative;
}

.display input {
    width: 100%;
    height: 80px;
    border: none;
    border-radius: 15px;
    padding: 20px;
    font-size: 2.8rem;
    font-weight: 300;
    text-align: right;
    background: var(--display-bg);
    color: var(--display-color);
    box-shadow: inset 0 4px 10px rgba(0, 0, 0, 0.2);
    letter-spacing: 1px;
    overflow: hidden;
    text-overflow: ellipsis;
}


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

/* buttons style */
.btn {
    padding: 20px 10px;
    border: none;
    border-radius: 15px;
    background: var(--btn-bg);
    color: var(--btn-color);
    font-size: 1.4rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.1), transparent);
}

.btn:hover::before {
    left: 100%;
}

.btn:hover {
    background: var(--btn-hover);
}

/* different buttons */
.operator {
    background: var(--operator-bg);
    color: var(--operator-color);
    font-size: 1.5rem;
}

.operator:hover {
    background: var(--operator-bg);
    opacity: 0.9;
}

.equal {
    background: var(--equal-bg);
    color: white;
    font-size: 1.6rem;
}

.equal:hover {
    background: var(--equal-hover);
}

.zero {
    grid-column: span 2;
}

.clear {
    background: var(--clear-bg);
    color: white;
    font-weight: 600;
}

.clear:hover {
    background: var(--clear-hover);
}

.back {
    background: var(--back-bg);
    color: var(--back-color);
    padding: 15px;
}

.back svg {
    fill: var(--back-color);
}

.back:hover {
    background: var(--back-hover);
}