/* =========================================
   RESET
========================================= */

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


/* =========================================
   BODY
========================================= */

body {
    min-height: 100vh;

    display: flex;
    justify-content: center;
    align-items: center;

    font-family: Arial, Helvetica, sans-serif;

    color: white;

    background:
        radial-gradient(
            circle at 10% 10%,
            #4b1979,
            transparent 35%
        ),
        radial-gradient(
            circle at 90% 90%,
            #00505c,
            transparent 35%
        ),
        linear-gradient(
            135deg,
            #080b1a,
            #171b38,
            #080b1a
        );

    overflow-x: hidden;
}


/* =========================================
   MAIN CONTAINER
========================================= */

.container {
    width: 520px;
    max-width: 94%;

    padding: 35px;

    text-align: center;

    position: relative;
    z-index: 10;

    border-radius: 30px;

    background:
        rgba(255, 255, 255, 0.08);

    border:
        1px solid rgba(255, 255, 255, 0.18);

    backdrop-filter: blur(18px);
    -webkit-backdrop-filter: blur(18px);

    box-shadow:
        0 30px 70px rgba(0, 0, 0, 0.6),
        inset 0 1px 1px
        rgba(255, 255, 255, 0.2);

    transform:
        perspective(1200px)
        rotateX(3deg);
}


/* =========================================
   TITLE
========================================= */

h1 {
    font-size: 48px;

    margin-bottom: 5px;

    background:
        linear-gradient(
            90deg,
            #ff00cc,
            #7b2cff,
            #00c6ff,
            #00ff88,
            #ffff00
        );

    background-size: 300% 300%;

    -webkit-background-clip: text;
    background-clip: text;

    -webkit-text-fill-color: transparent;

    animation:
        titleColor 5s ease infinite;

    text-shadow:
        0 10px 25px
        rgba(0, 0, 0, 0.5);
}


h2 {
    font-size: 20px;

    margin-bottom: 15px;

    color: #00ffff;

    text-shadow:
        0 0 12px #00ffff;
}


/* =========================================
   DESCRIPTION
========================================= */

.description {
    color: #d7d7d7;

    line-height: 1.5;

    margin-bottom: 25px;
}


/* =========================================
   SUDOKU GRID
========================================= */

.sudoku-grid {
    width: 405px;
    height: 405px;

    max-width: 100%;

    margin: 0 auto 25px;

    display: grid;

    grid-template-columns:
        repeat(9, 1fr);

    grid-template-rows:
        repeat(9, 1fr);

    background: #101329;

    border: 4px solid #00ffff;

    border-radius: 8px;

    overflow: hidden;

    box-shadow:
        0 15px 35px
        rgba(0, 0, 0, 0.6),

        0 0 25px
        rgba(0, 255, 255, 0.25),

        inset 0 0 20px
        rgba(0, 255, 255, 0.1);
}


/* =========================================
   CELLS
========================================= */

.cell {
    width: 100%;
    height: 100%;

    border: 1px solid
        rgba(255, 255, 255, 0.25);

    outline: none;

    text-align: center;

    font-size: 24px;
    font-weight: bold;

    color: white;

    background:
        rgba(255, 255, 255, 0.04);

    transition:
        background 0.2s,
        box-shadow 0.2s;
}


/* =========================================
   3x3 BOX BORDERS
========================================= */

/* Vertical borders after columns 3 and 6 */

.cell:nth-child(3n) {
    border-right: 3px solid #00ffff;
}


/* Horizontal borders after rows 3 and 6 */

.cell:nth-child(n + 19):nth-child(-n + 27),
.cell:nth-child(n + 46):nth-child(-n + 54) {
    border-bottom: 3px solid #00ffff;
}


/* =========================================
   INPUT EFFECT
========================================= */

.cell:hover {
    background:
        rgba(0, 255, 255, 0.12);
}


.cell:focus {
    background:
        rgba(0, 255, 255, 0.20);

    box-shadow:
        inset 0 0 15px
        rgba(0, 255, 255, 0.6);
}


/* =========================================
   SOLVED CELLS
========================================= */

.cell.solved {
    color: #00ff88;

    background:
        rgba(0, 255, 136, 0.12);

    text-shadow:
        0 0 10px #00ff88;

    animation:
        solvedCell 0.4s ease;
}


/* =========================================
   BUTTONS
========================================= */

.buttons {
    display: flex;

    justify-content: center;

    gap: 15px;

    flex-wrap: wrap;
}


button {
    min-width: 150px;

    padding: 14px 22px;

    border: none;

    border-radius: 12px;

    font-size: 16px;

    font-weight: bold;

    color: white;

    cursor: pointer;

    background:
        linear-gradient(
            135deg,
            #ff00cc,
            #7b2cff,
            #0066ff
        );

    box-shadow:
        0 7px 0 #17103f,
        0 15px 25px
        rgba(0, 0, 0, 0.4);

    transition:
        transform 0.2s,
        box-shadow 0.2s;
}


button:hover {
    transform:
        translateY(-3px);

    box-shadow:
        0 10px 0 #17103f,
        0 20px 30px
        rgba(0, 0, 0, 0.5);
}


button:active {
    transform:
        translateY(4px);

    box-shadow:
        0 3px 0 #17103f;
}


/* =========================================
   MESSAGE
========================================= */

#message {
    min-height: 30px;

    margin-top: 25px;

    font-size: 18px;

    font-weight: bold;
}


.success {
    color: #00ff88;

    text-shadow:
        0 0 15px #00ff88;
}


.error {
    color: #ff4d6d;

    text-shadow:
        0 0 15px #ff4d6d;
}


/* =========================================
   3D BACKGROUND SHAPES
========================================= */

.shape {
    position: fixed;

    width: 120px;
    height: 120px;

    border-radius: 30px;

    opacity: 0.15;

    z-index: 1;

    pointer-events: none;

    animation:
        floating 7s infinite ease-in-out;
}


.shape-one {
    top: 8%;
    left: 8%;

    background:
        linear-gradient(
            135deg,
            #ff00cc,
            #7b2cff
        );

    transform:
        rotate(25deg);
}


.shape-two {
    right: 8%;
    bottom: 10%;

    background:
        linear-gradient(
            135deg,
            #00ffff,
            #0066ff
        );

    animation-delay: 2s;
}


.shape-three {
    right: 15%;
    top: 15%;

    background:
        linear-gradient(
            135deg,
            #00ff88,
            #ffff00
        );

    animation-delay: 4s;
}


/* =========================================
   ANIMATIONS
========================================= */

@keyframes floating {

    0%,
    100% {
        transform:
            translateY(0)
            rotate(0deg);
    }

    50% {
        transform:
            translateY(-45px)
            rotate(180deg);
    }
}


@keyframes titleColor {

    0% {
        background-position: 0% 50%;
    }

    50% {
        background-position: 100% 50%;
    }

    100% {
        background-position: 0% 50%;
    }
}


@keyframes solvedCell {

    0% {
        transform: scale(0.5);
        opacity: 0;
    }

    100% {
        transform: scale(1);
        opacity: 1;
    }
}


/* =========================================
   MOBILE
========================================= */

@media (max-width: 550px) {

    .container {
        padding: 22px;
    }

    h1 {
        font-size: 36px;
    }

    h2 {
        font-size: 17px;
    }

    .sudoku-grid {
        width: 100%;
        height: auto;

        aspect-ratio: 1 / 1;
    }

    .cell {
        font-size: 18px;
    }

    button {
        min-width: 130px;

        padding: 12px 15px;

        font-size: 14px;
    }
}