:root {
    --body-bg: #ffffff;
    --header-bg: #ffffff;
    --border-color: #434343;
    --first-block: #cccccc;
    --second-block: #f4f4f4;

    --text-color: #000000;
    --button-bg: #000000;
    --button-color: #ffffff;
}

html, body {
    margin: 0;
    padding: 0;
    font-family: Calibri, "sans-serif";
}

body {
    display: flex;
    flex-direction: column;
    background-color: var(--body-bg);
}

.header {
    height: 50px;
    width: 60%;
    margin: 0 auto;
    background-color: var(--header-bg);
    display: flex;
    align-items: center;
    padding: 0 10px;
    justify-content: space-between;
    line-height: 50px;
    border: 2px solid var(--border-color);
}

.btn {
    display: inline-block;
    width: 10px;
    height: 40px;
    line-height: 40px;
    text-align: center;
    text-decoration: none;
    color: var(--button-color);
    font-weight: bold;

    border-radius: 4px;
    background-color: var(--button-bg);
    transition: background-color 0.3s ease;
    cursor: pointer;
}

.main {
    height: 100%;
    width: 60%;
    margin: 0 auto;
    text-align: center;
    background-color: var(--body-bg);
    color: var(--text-color);
    padding: 10px;
    border: 2px solid var(--border-color);
}