* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
    margin: 0;
    padding: 0;
    background: #d8d6cf;
    color: #222;
    font: 13px/1.45 Arial, Tahoma, Verdana, sans-serif;
}

a {
    color: #064b9b;
    text-decoration: underline;
}

a:hover { color: #a12727; }

.site {
    width: 1040px;
    max-width: calc(100% - 14px);
    margin: 7px auto;
    background: #fff;
    border: 1px solid #777;
}

.service {
    padding: 4px 8px;
    background: #efeee9;
    border-bottom: 1px solid #aaa;
    color: #666;
    font-size: 11px;
}

.header {
    width: 100%;
    border-collapse: collapse;
    background: #f8f8f4;
}

.header td {
    padding: 9px 10px;
    vertical-align: middle;
}

.logo-cell { width: 62%; }

.logo {
    margin: 0;
    font: bold 27px Georgia, "Times New Roman", serif;
    color: #213e68;
}

.logo a {
    color: #213e68;
    text-decoration: none;
}

.logo b { color: #8f3e35; }

.slogan {
    margin-top: 2px;
    color: #666;
    font-size: 11px;
}

.header-info {
    text-align: right;
    color: #555;
    font-size: 11px;
}

.main-menu {
    width: 100%;
    border-collapse: collapse;
    background: #314f78;
    border-top: 1px solid #1f385b;
    border-bottom: 1px solid #1f385b;
}

.main-menu td {
    padding: 0;
    border-right: 1px solid #6f87a6;
}

.main-menu td:last-child { border-right: 0; }

.main-menu a {
    display: block;
    padding: 7px 10px;
    color: #fff;
    font-weight: bold;
    text-decoration: none;
    text-align: center;
}

.main-menu a:hover { background: #456892; }

.submenu {
    padding: 5px 8px;
    background: #e9e4d6;
    border-bottom: 1px solid #b9b39f;
    font-size: 11px;
}

.submenu a { margin-right: 13px; }

.breadcrumbs {
    padding: 5px 8px;
    background: #f8f8f5;
    border-bottom: 1px solid #ccc;
    color: #666;
    font-size: 11px;
}

/* В DOM: main -> left -> right.
   На десктопе CSS визуально ставит left | main | right. */
.layout {
    display: grid;
    grid-template-columns: 190px minmax(0, 1fr) 220px;
    grid-template-areas: "left main right";
    align-items: start;
}

main.content {
    grid-area: main;
    min-width: 0;
    padding: 10px 12px 18px;
}

aside.left {
    grid-area: left;
    padding: 8px;
    background: #f3f3ef;
    border-right: 1px solid #bbb;
}

aside.right {
    grid-area: right;
    padding: 8px;
    background: #faf9f5;
    border-left: 1px solid #bbb;
}

h1 {
    margin: 0 0 8px;
    color: #1f3554;
    font: bold 24px Georgia, "Times New Roman", serif;
}

h2 {
    margin: 16px 0 7px;
    padding-bottom: 2px;
    border-bottom: 1px solid #a9a9a4;
    color: #7c342f;
    font-size: 17px;
}

h3 {
    margin: 12px 0 5px;
    color: #334763;
    font-size: 14px;
}

p { margin: 6px 0; }

.side-box {
    margin-bottom: 9px;
    border: 1px solid #9d9d98;
    background: #fff;
}

.side-title {
    padding: 4px 6px;
    background: #dce3ea;
    border-bottom: 1px solid #9d9d98;
    color: #253f61;
    font-weight: bold;
}

.side-title.red {
    background: #eadedb;
    color: #6d302c;
}

.side-links {
    margin: 0;
    padding: 5px 7px 6px 20px;
}

.side-links li { margin: 3px 0; }

.small {
    color: #666;
    font-size: 11px;
}

.lead {
    padding: 7px;
    border: 1px solid #aaa;
    background: #fffff1;
}

.solve-box {
    margin: 10px 0 13px;
    border: 1px solid #777;
    background: #f5f5f2;
}

.solve-head {
    padding: 5px 7px;
    background: #d8dde3;
    border-bottom: 1px solid #777;
    color: #263c58;
    font-weight: bold;
}

.solve-body { padding: 8px; }

.equation-line {
    display: flex;
    gap: 7px;
    align-items: center;
    flex-wrap: wrap;
}

.eq-input {
    width: 280px;
    max-width: 100%;
    padding: 6px;
    border: 1px solid #777;
    background: #fff;
    font: 15px "Courier New", monospace;
}

.old-button {
    padding: 6px 11px;
    border: 1px solid #666;
    border-top-color: #eee;
    border-left-color: #eee;
    background: #d8d8d5;
    color: #111;
    font: bold 12px Arial, sans-serif;
    cursor: pointer;
}

.old-button:active {
    border: 1px solid #666;
    border-right-color: #eee;
    border-bottom-color: #eee;
}

.result {
    margin-top: 8px;
    padding: 7px;
    border: 1px solid #aaa;
    background: #fffbe3;
    min-height: 55px;
}

.rule-table,
.example-table,
.topic-table,
.class-table {
    width: 100%;
    border-collapse: collapse;
    margin: 8px 0;
}

.rule-table th, .rule-table td,
.example-table th, .example-table td,
.topic-table th, .topic-table td,
.class-table th, .class-table td {
    padding: 6px;
    border: 1px solid #aaa;
    vertical-align: top;
}

.rule-table th,
.example-table th,
.topic-table th,
.class-table th {
    background: #e8e8e5;
    text-align: left;
}

.step {
    width: 52px;
    text-align: center;
    background: #f4ead3;
    color: #6b512d;
    font-weight: bold;
}

.note {
    margin: 8px 0;
    padding: 7px;
    border: 1px solid #b9a377;
    background: #fff8de;
}

.error {
    margin: 8px 0;
    padding: 7px;
    border: 1px solid #bd918a;
    background: #fff0ee;
}

.footer {
    padding: 8px;
    border-top: 1px solid #777;
    background: #ecebe7;
    color: #666;
    text-align: center;
    font-size: 11px;
}

@media (max-width: 780px) {
    body {
        background: #fff;
        font-size: 14px;
    }

    .site {
        width: auto;
        max-width: none;
        margin: 0;
        border: 0;
    }

    .service { display: none; }

    .header,
    .header tbody,
    .header tr,
    .header td {
        display: block;
        width: 100%;
    }

    .header-info {
        text-align: left;
        padding-top: 0 !important;
    }

    .main-menu,
    .main-menu tbody,
    .main-menu tr {
        display: block;
        width: 100%;
    }

    .main-menu tr {
        display: grid;
        grid-template-columns: 1fr 1fr;
    }

    .main-menu td {
        display: block;
        border-bottom: 1px solid #6f87a6;
    }

    .main-menu a {
        text-align: left;
        padding: 9px;
    }

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

    main.content {
        order: 1;
        width: 100%;
        padding: 9px;
    }

    aside.left {
        order: 2;
        width: 100%;
        border-right: 0;
        border-top: 1px solid #bbb;
    }

    aside.right {
        order: 3;
        width: 100%;
        border-left: 0;
        border-top: 1px solid #bbb;
    }

    .eq-input {
        width: 100%;
        font-size: 16px;
        padding: 8px;
    }

    .old-button {
        padding: 8px 12px;
        font-size: 14px;
    }

    h1 { font-size: 22px; }
}

.coef,.system-inputs input{width:70px;padding:6px;border:1px solid #777;background:#fff;text-align:center;font:14px Arial,sans-serif}.system-inputs{border-collapse:collapse;margin:6px 0}.system-inputs td{padding:4px}.formula{margin:8px 0;padding:8px;border:1px solid #aaa;background:#f7f7f2;text-align:center;font:bold 17px Georgia,serif}.related-list{margin:0;padding-left:20px}.related-list li{margin:6px 0}.trainer-levels{display:flex;gap:5px;flex-wrap:wrap;margin-bottom:7px}.trainer-levels button{padding:4px 7px;border:1px solid #777;background:#eee;cursor:pointer}.task-math{padding:8px;margin-bottom:7px;border:1px solid #aaa;background:#fff;font:bold 18px Georgia,serif}.ad-slot{margin:8px 0;padding:5px;border:1px dashed #bbb;color:#777}.search-results li{margin:8px 0}.field-note{font-size:11px;color:#666}
@media(max-width:780px){.coef,.system-inputs input{width:90px;max-width:28vw;font-size:16px}.trainer-levels button{padding:8px}}

/* v1.1 content/SEO utility blocks */
.useful-box,.check-box{margin:9px 0;padding:7px 9px;border:1px solid #aaa;background:#f5f7f8}
.useful-box{border-color:#a5ad9c;background:#f5f7ef}
.check-box{border-color:#9eabbc;background:#f1f5f9}
.useful-box b,.check-box b{color:#334763}
.useful-box ul,.check-box ul{margin:5px 0 0;padding-left:20px}
.useful-box li,.check-box li{margin:3px 0}
.semantic-note{font-size:11px;color:#666;margin:5px 0}